The Hemiuroidea terminology, systematics and : evolution David Ian Gibson and Rodney Alan Bray Zoology Department, British Museum (Natural History), Cromwell Road, London SW7 5BD Contents ............ .......... ... ............ ............ ........... ............ ............ ........... ............ ........... Synopsis Introduction Definitions of hemiuroid structures with comments on their systematic value II. and possible function III. A classification of the Hemiuroidea with keys and definitions. Introduction I. Azygiidae Bathycotylidae Bunocotylidae 39 54 54 55 57 60 62 62 Derogenidae 71 Hemiuroidea Accacoeliidae Dictysarcidae Hemiuridae Hirudinellidae Isoparorchiidae Lecithasteridae Ptychogonimidae . . . . . . . . . . . . . . . . . . . . . Sclerodistomidae Sclerodistomoididae . . . . . . . . . . . . . . . . . . . A . . . A . . . . . . . . . . . . 84 98 114 114 .116 .118 .130 .... . . 133 135 Acknowledgements References 81 .100 .101 .110 .111 Syncoeliidae Generic index to part III. discussion on the evolution of the Hemiuroidea. Evolutionary trends in the Hemiuroidea suggested evolutionary scheme within the Hemiuroidea Some comments on the relationship of the Didymozooidea and the Paramphistomoidea to the Hemiuroidea . IV. 35 36 . . . .135 Synopsis The history of the classification of the Hemiuroidea and the features which have been used as criteria for distinguishing the higher taxa, such as adult morphology, life-cycle patterns and cercarial anatomy, are discussed. It is suggested that the best basic criterion currently available is the functional morphology of the adult. Explanations of the terminology with comments on the systematic significance and possible function of the features used in the study of hemiuroid taxonomy are included. A classification of the Hemiuroidea is presented with keys and definitions of the taxa to the generic level. The classification and definitions are based, where possible, on original observations of sectioned material. The Hemiuroidea is divided into fourteen families. The Accacoeliidae contains the Accacoeliinae and Paraccacladiinae, the latter subfamily consisting of only one genus. The Azygiidae consists of two subfamilies, the Azygiinae and Leuceruthrinae. The Bathycotylidae, Isoparorchiidae and Ptychogonimidae contain single genera, while the Hirudinellidae contains three monotypic genera. The Bunocotylidae is Bull. Br. Mus. not. Hist. (Zool.) 36 (2) : 35-146 Issued 26 July, 1979 36 D. I. GIBSON & R. A. BRAY and contains the Bunocotylinae, Aphanurinae, Opisthadeninae (including Neotheletrum gen. and Theletrinae subfam. nov. The Derogenidae is also redefined and contains the Derogeninae, Gonocercinae and Halipeginae. The hemiuroids from the teleost swim-bladder, with the exception of Isoparorchis, are placed in the Dictysarcidae, which is composed of the Dictysarcinae, Albulatrematinae and Cylindrorchiinae subfam. inq. The Hemiuridae is restricted to ecsomate forms and contains the redefined nov.) following subfamilies: Hemiurinae, Dinurinae, Elytrophallinae, Glomericirrinae, Hypohepaticolinae, Lecithochiriinae, Lethadeninae, Plerurinae subfam. nov. and Pulmoverminae. The Lecithasteridae is redefined and is composed of the Lecithasterinae, Hysterolecithinae (including Thulinia gen. nov.), Macradeninae, Prolecithinae, Quadrifoliovariinae and Trifoliovariinae. The Sclerodistomidae contains the Sclerodistominae, Prosogonotrematinae and Prosorchiinae. The Sclerodistomoididae fam. nov. is erected for Sclerodistomoides, and in the Syncoeliidae, the Syncoeliinae and Otiotrematinae are redefined. An index to the generic names used in this classification is included. The criteria which may be used as indicators of the relative 'primitiveness' of various taxa or to illustrate phylogenetic relationships within the group are discussed. In relation to this, evolutionary trends within three organ-systems, (1) the seminal storage and disposal apparatus in the female reproductive system, (2) the vitellarium and (3) the terminal genitalia, are studied in detail. Using evidence from this study, an evolutionary picture for the Hemiuroidea is presented, and its relationships with the Didymozooidea and the Paramphistomoidea are commented upon. I. Introduction The superfamily Hemiuroidea Looss, 1899, is a group within the Digenea which includes species usually parasitic in the gut, particularly in the stomach, of fishes. They are found predominantly in marine teleosts, but also occur in freshwater teleosts, elasmobranchs and occasionally in amphibians and reptiles. It is not unusual for progenetic forms to occur in molluscs and other marine, and occasionally freshwater, invertebrates. In addition to the alimentary canal of fishes, examples are known from the gall-bladder, swim-bladder, body-cavity, mouth, gills and from the skin, whilst all known species of one group are found in the lung of sea-snakes. Overall, the hemiuroids form a very diverse group, not only in habitat, but also in morphology. Indeed, the wide variations in adult morphology, even within proposed higher taxa, have resulted in a good deal of confusion with regard to the validity, composition and systematic relationships of these taxa. The superfamily was erected, under the name Hemiurida, by Dollfus (1923), and comprised the families Hemiuridae, Accacoeliidae and Syncoeliidae. Prior to this Looss (1907, 1908) had carefully re-described many species of hemiuroids and set a basic pattern on which later authors, notably Odhner (1911), Poche (1926) and Fuhrmann (1928), were able to build. These early workers based their classifications entirely upon adult morphology and divided the group into a small number of families, although not always indicating the relationships between these families. Odhner (1911), for example, grouped three families together, the Hemiuridae, Azygiidae and Didymozoidae. Since Odhner, the concept of the Hemiuridae has been sub-divided, condensed and sub-divided again on numerous occasions. Systematic histories of the Hemiuroidea have been compiled by Chauhan (1954), Skrjabin & Guschanskaja (1954, 1956, 1960) and more recently by Stunkard (1973), although the latter author has omitted the important contributions of Chauhan (1954), Manter & Pritchard (19600) and Mehra (1962). In order to avoid repetition, we have condensed several of the more recent conceptions of the Hemiuroidea in the form of can be seen from this table that Odhner's original conception was split by Yamaguti into three superfamilies and eighteen families, one of which, the Hemiuridae, contains (1971) The large number of higher taxa in this rather uncritical work of Yamasubfamilies. twenty-five guti appears to be the result of the acceptance of inadequate descriptions as being accurate. Table 1. It Stunkard (1973) summarized the problem succinctly as follows: 'in the course of the past hundred years, a large number of trematodes have been described, many on inadequate and erroneous information and based often on a single specimen. New genera and higher taxonomic categories have been erected to receive these dubious species.' Yamaguti, for example, has accepted three genera in three different families for forms which we consider to be synonymous with the genus Elongoparorchis Rao, 1961. Recent conceptions of the Hemiuroidea, and of the Digenea in general, have been greatly THE HEMIUROIDEA 37 38 D. I. GIBSON & BRAY R. A. work of La Rue (1957), who sub-divided the Digenea into two groups, the Epitheliocystidia and the Anepitheliocystidia, depending upon the epithelial or membranous nature of the lining of the cercarial excretory vesicle. The Azygiidae was placed in the latter group, while the remainder of the hemiuroids with 'known' life-histories were placed in the former. This influenced by the resulted in the majority of recent workers considering the Azygiidae to be distinct from the Hemiuroidea, at least at the superfamily level (see Odening, 1974). Work by Powell (1972, 1973, 1975) and Gibson (1974) indicated that it is likely that all cercariae have a syncytial lining work has to the excretory vesicle. This casts grave doubts upon the validity of La Rue's conceptions. Yamaguti (1971) stated that life-cycle patterns may be an important systematic feature; but, due to a lack of knowledge with regard to the life-histories of this group, this aspect appears to be of little use in its classification. The little that is known suggests that, even within one family, Buttner, 1959; Sinclair et al., 1973; the life-cycle can vary considerably in detail (see Chabaud Bray & Gibson, 1977). Stunkard (1973) gave a useful four-page summary of the present knowledge of the hemiuroid life-cycle, and Yamaguti (1975) lists much of this information in more detail. Stunkard introduced his contribution as follows The wide divergence of opinion concerning & : the systematics and classification of the hemiuroid trematodes is the result, in large measures, of lack of knowledge of their life-cycles and developmental stages. Data are meager, fragmentary, often faulty, and sometimes erroneous.' He summarized his findings thus: 'The miracidia of the hemiuroid, azygiid and didymozoid species are unique and very similar. All are aciliate, provided The cercariae with an anterior circle of spines, and the surface of the body bears bristles and into the cystoand lack in develop glands, cystogenous rediae; penetration they develop phorous stage which is characteristic for hemiurid trematodes. Typically they are eaten by copepods and the metacercariae occur as unencysted larvae in the hemocoel of the crustaceans or The striking similarity of the larval other planktonic invertebrates that feed on copepods . . . . . . homostages, and the fact that they are peculiar to the hemiurid trematodes, portends genetic and Fiihrmann geneity and despite adult adaptations to different situations, the thesis of Odhner that the Azygiidae, Hemiuridae and Didymozoidae are closely related is probably correct'. We agree that these groups do seem to be closely related, although we are reluctant to place too much emphasis on larval stages, especially considering the recent work of Devaraj (1972) and Schell (1975), who have described ciliated, non-spinous miracidia for the hemiuroids Isoparorchis hypselobagri (Billet, 1898) and Lecithaster salmonis Yamaguti, 1934, respectively. Similarly, a small number of cystophorus cercaria such as, Cercaria vaullegeardi Pelseneer, 1906, are known are not convinced of the to develop in daughter-sporocysts and not rediae (see Popiel, 1976). primitive nature of the cercaria relative to the adult, because of the morphological similarities We between what we consider to be primitive hemiuroids and the aspidogastreans (see below). The hypothesis that the present adult digenean evolved from a mature, free-swimming cercaria-like adult is presented by Cable (1965, 1974). It appears more likely to us that the adult forms from vertebrates arose directly from primitive molluscan parasites, in much the same way as many aspidogastreans, and that the crustacean host and the cercarial stage are more recent developments. Pearson (1972) and Rohde (1972) discuss the two contrasting hypotheses concerning the evolutionary significance of the digenean life-cycle. It seems likely that the morphological differences in cercariae, hitherto used as systematic indicators, are, at least to some extent, the result of the is benthic, then ecological requirements of the life-history. If, for example, the crustacean host has a which a that of to a different the cercarial tail will tend to be of pelagic crustaspecies shape cean host. In other superfamilies, such as the Allocreadioidea, there appear to be major differences similar argument also applies when considering the in the cercariae of different families. A chaetotaxy of cercariae as a systematic criterion. In the latter case there is no reason why the hypertrophy or atrophy of the nervous system does not depend upon the ecological requirements of the life-history. One additional disadvantage in using larval characteristics or life-history for systematic purposes, is that for the majority of determinations only adult-specimens are available for study. The lack of knowledge with regard to the larval stages and life-histories of the great majority of genera, however, remains the greatest limitation to their value in systematics. We suggest, therefore, that the use of life-history details, and particularly cercarial morphology, should be treated with at least as much caution as the use of adult morphology. THE HEMIUROIDEA 39 We consider that neither the gross morphology of the adult, due to its variability, nor the use of life-cycle patterns and cercarial morphology, due to a lack of knowledge and understanding with regard to their significance, are able to provide us with a satisfactory classification. In our opinion, morphology appears to offer the best alternative. In order to use this concept, one must have a detailed knowledge of the morphology of an organ or organ-system and an understanding of its probable function. Once its function is understood, one can then comprehend the requirements for such an organ in order that the animal might complete its life-history. With an understanding of the function and requirement for particular organs and organ-systems, one can rationalize many of the diverse variations which occur in different taxa, and recognize where development or atrophy has occurred. This sheds light, not only upon the systematics, but also upon the phylogenetic relationships of the taxa. It also tends to expose inaccurate descriptions and is a useful aid in suggesting the probable structure of particular organs in inadequately described taxa. The following classification, which we propose for the Hemiuroidea, is based, therefore, upon adult morphology associated with an attempted understanding of the function of organs and organ-systems. This functional aspect has permitted us to try and base our concepts upon a combination of features, rather than upon one critical feature. functional Definitions of hemiuroid structures* with comments on their systematic value and possible function Accessory excretory organ (vesicle) see Manter' s organ. II. Annulations or annular plications - see plications. - a type of seminal receptacle which does not communicate with the Blind seminal receptacle exterior via Laurer's canal, but which is linked to the oviduct by a short duct (Fig. 1) and usually has a thick wall. It serves as a seminal store, and its presence, except in the cases in the Tri- and Derogeninae where it appears to have arisen from a canalicular seminal receptaby the loss of Laurer's canal, appears to be a good systematic feature at the subfamily level. is worth noting that when a blind seminal receptacle is present, the uterine seminal receptacle foliovariinae cle It (q.v.) is lost. See seminal receptacle. Canalicular seminal receptacle - a large proximal dilation of Laurer's canal which is normally filled with fresh, as opposed to spent, spermatozoa (Fig. 1). This type of seminal receptacle (q.v.) in the majority of cases as a vagina (Gibson & is possibly a recent adaptation associated with the use of Laurer's canal Bray, 1975). See seminal receptacle. Cirrus - an intromittent copulatory organ which rare in hemiuroids, occurring only in the formed from or encloses the male duct only. the Hirudinellidae. Although its presence in certain other hemiuroid groups has been indicated in the literature, in two such cases, the hemiurid Glomericirrus and the derogenid Arnola, our observations of sectioned material show that this structure is definitely absent, there being a sinus-organ (q.v.) present. The occurrence of a cirrus in the Hemiuroidea, therefore, is most likely a feature of importance at the family It is level. It is unlikely, common in however, that the of Digenea. 'cirrus' is members of of the hirudinellids is homologous with the cirrus many groups Cirrus sac - a muscular sac which surrounds the terminal portion of the male duct including the cirrus. Its function appears to aid the eversion of the cirrus (q.v.) and the expulsion of spermait often encloses the seminal vesicle (q.v.), during copulation by exerting hydrostatic pressure upon its contents. It is to some extent, therefore, analogous with the sinus-sac (q.v.). This structure occurs in the Hirudinellidae: its reported presence in other hemiuroid groups, such as the Halipeginae, we consider to be extremely doubtful. The presence of a cirrus-sac is in tozoa, as our opinion a feature of importance at the family level in the Hemiuroidea. * It should be noted that a smaller glossary of terms used in hemiuroid systematics was produced by Manter (1970). There are, however, significant differences between some of our definitions and those of Manter. usr Fig. 1. The different types of seminal receptacle present in the receptacle; B. [bsr, blind seminal receptacle; csr, canalicular seminal receptacle; Lc, Laurer's rudimentary seminal receptacle; usr, uterine seminal receptacle.] seminal receptacle, canal; rsr, Hemiuroidea: A. Uterine seminal receptacle; D. Blind Rudimentary seminal receptacle; C. Canalicular seminal THE HEMIUROIDEA 41 Cyclocoel the name given to the gut-caeca when fused terminally, thus forming a complete caecal ring. The advantage of this caecal arrangement is unknown. This feature is of generic importance only, as it occurs widely in unrelated groups both within and outside the Hemiuroidea. The apparent cyclocoel found in large specimens of Hirudinella appears to be a subterminal fusion of the gut-caeca which takes place during the development of the animal. DrUsenmageri - this structure, the name of which means 'glandular stomach', is found at the 'shoulder'-region of the gut-caeca in many hemiuroids. It is usually an expanded region lined by large, glandular cells forming a villous luminal surface, which is readily distinguished from the lining of the remainder of the caecum. Its function is not known, but it is probably a region of specialized secretion and/or digestion. It does not appear to be of systematic significance as it 1 ' occurs widely in distantly related hemiuroids, but it (1970) refers to these structures as 'precaecal sacs'. is apparently absent in the azygiids. Manter Ecsoma - this is the name given to the posterior region of the body of an adult digenean, when it capable of being retracted within the body (soma). This structure, which appears to be unique to the Hemiuridae, is occasionally referred to as a 'tail' or the specimens are referred to as 'appendiculate' or 'ecsomate'. The gut-caeca, uterus and, on rare occasions, the ovary and vitellarium may extend into the ecsoma, and the excretory pore opens terminally on it. The mechanism of extension is not known, although the body-wall clearly contains longitudinal and circular muscles; but within the ecsoma are numerous large, vesicular cells which might be involved with this process, acting as a hydrostatic skeleton. Its function is thought to be that of a feeding organ which is extruded during periods when the pH or the osmolarity of the stomach contents is at a tolerable level. It should be noted that hemiurids tend to occur in the lumen of the stomach, is marine teleosts and are, therefore, subject to great variations in and osmolarity (MacKenzie & Gibson, 1970). We suggest that other groups present in the stomach of these fish, such as the derogenines, tend to live more in the cardiac end of the stomach and only migrate down into the lumen during periods of more neutral pH and/or low osmolarity. These suggestions are made on the basis of observations of Derogenes varicus and Hemiurus communis. In relation to this function, the development of the ecsoma appears to be associated with the development of plications (q.v.) of the tegument. As the ecsoma occurs only in the hemiurids, this feature is of importance at the family level. In some groups, however, such as in some of the lecithochiriine genera, the ecsoma may be reduced especially the pyloric region, of pH in size. Egg-filaments in a few hemiuroids the egg-shell may be drawn out at the poles to form filaments. Usually, these are unipolar and may be of variable length. Occasionally, they are bipolar and may bear more than one filament (e.g. Anguillotrema). It is likely that these filaments are part of a mechanism associated with the acquisition of the first intermediate host. They may, for example, become attached to the gill-filaments of the mollusc. In the case of Hypohepaticola, which tends to be a tissue-parasite, the spine-like filament may aid the exit of the egg from the tissue by a mechanism similar to that found in schistosomes. The presence of egg-filaments is a feature of only generic importance, as it occurs spasmodically throughout the group, particularly in the Derogenidae. - the entire male duct distal to the seminal vesicle can theoretically be referred Ejaculatory duct to as the ejaculatory duct. Regions such as the pars prostatica (q.v.) and cirrus (q.v.) are modifications of the ejaculatory duct. In the hemiuroids, however, the region generally referred to as the ejaculatory duct name. is When present, an unmodified region of this duct and is, therefore, without an alternative occurs between the pars prostatica and the hermaphroditic duct (q.v.) [or it terminus of the male system]. It may occur entirely or partly inside or outside the sinus-sac (q.v.). This region of the duct is of little systematic importance, except perhaps at the specific level but it is long in certain lecithasterids, especially in the Macradenininae. Occasionally, unmodified regions of the male duct occur between the seminal vesicle and the pars prostatica or separating two regions of the pars prostatica. These regions, however, are not referred to as the ejaculatory duct, but usually as tubular extensions of the seminal vesicle or aglandular regions of the pars ; prostatica. 42 D. I. GIBSON & R. A. BRAY Ejaculatory vesicle a dilation of the ejaculatory duct (q.v.) within the sinus-sac (q.v.). This feature occurs in certain lecithochiriine genera and, in its glandular form (see prostatic vesicle), in the Glomericirrinae, Hysterolecithinae and the remainder of the lecithochiriines. It appears to function as a small seminal reservoir as part of a mechanism to increase the amount of sperma- & tozoa ejected from the sinus-sac during copulation. Nasir Diaz (1971) suggest that an ejaculatory vesicle is merely a prostatic vesicle from which the cellular lining has been lost, hence we suggest that it might be more appropriate to refer to the prostatic vesicle as a 'glandular ejaculatory vesicle' (see p. 93). The presence of an ejaculatory vesicle or a glandular ejaculatory vesicle (prostatic vesicle) is a feature of importance at the subfamily level. - Excretory vesicle (bladder) in hemiuroids this is essentially Y-shaped, the arms often uniting dorsally to the pharynx or oral sucker. The presence of blind arms is a feature of no more than generic importance, as it appears to occur widely in distantly related forms, and indeed we have not used it at the generic level in the case of the azygiid genus Otodistomum. There are a number of modifications of the basic structure of this organ, especially in the stouter hemiuroids. These include: (1) in the Sclerodistomidae there are one or two Manter's organs (q.v.), often called 'accessory excretory vesicles', which communicate with this organ distally; (2) in Hirudinella, Botulus and Sclerodistomum the arms form a branching system of tubules or diverticula; (3) in some of the primitive groups, such as the Accacoeliidae, Hirudinellidae and Syncoeliidae, the excretory arms are usually arranged so that initially they pass forward dorsally and ventrally^ instead of laterally and (4) in the Ptychogonimidae the excretory arms unite twice in the forebody ; Fischthars organ - this is a name given by Yamaguti (1971) for a round vesicle of unknown function, lined with epithelial cells and surrounded by a dense mass of gland-cells, which apparently opens dorsally to the right of Mehlis' gland (q.v.) in Pelorohelmins palawanensis Fischthal & Kuntz, 1964. There is no evidence of such a structure in specimens under the name of P. ghanensis Fischthal & Thomas, 1968, from the collection of the British Museum (Natural History). It is possible, therefore, that Yamaguti may have mistaken Juel's organ (q.v.) for this structure. He Kuntz, 1964, a species however, describes this structure in Meristocotyle varani Fischthal also, & unknown relationship; but in this case it is the distal dilation of Laurer's canal which opens dorsally. [We should point out that we regard Pelorohelmins to be a synonym of Elongoparorchis.] of Genital atrium - a receptacle present in most hemiuroids between the hermaphroditic duct and the genital pore, which probably acts as a vagina during copulation. Spermatozoa are probably deposited within this structure by the copulatory organ of another worm when cross-insemination occurs, and it is then either sucked back into the hermaphroditic duct by the action of the sinus- more likely, forced back (the sinus-organ being retracted to receive it) by the action of the muscular walls of the genital atrium which are contractile. The lining of the genital atrium is continuous with the sinus-organ (or in the case of the hirudinellids, the 'cirrus'), and appears to contribute significantly to the formation of its outer surface as it extends. In some of the hirudinellids the genital atrium may be everted through the genital pore, thus giving extra length to the 'cirrus' (see Fig. 12D of Gibson & Bray, 1977). This also occurs in Isoparorchis (Fig. 2), where it adds additional length to the sinus-organ. The contractile nature of this organ makes it of limited taxonomic value, even at the specific level, although its apparent total absence may be of some value. It is often reduced or absent in species which must rely upon self-insemination or which possess only a temporary sinus-organ. When the sinus-organ and sinus-sac are absent, it is difficult to distinguish the genital atrium from the hermaphroditic duct. In such cases, these two terms often appear to have been used intersac or, changeably. Genital pore - the aperture through which the contents of the genital ducts pass to the exterior. It usually, in the Hemiuroidea, forms the mouth of the genital atrium, but occasionally occurs at the distal end of the hermaphroditic duct, when the genital atrium (q.v.) is absent, or at the union of the male and female ducts when both the hermaphroditic duct and the genital atrium are absent. The genital pore is not always the most distal part of the terminal genital apparatus, as during copulation the copulatory organ, or even the genital atrium, is thrust through the genital THE HEMIUROIDEA Fig. 2 Sagittal sections 43 through the terminal genitalia of Isoparorchis A. Withdrawn; B. Extruded, [so, sinus-organ; wga, wall of genital atrium.] : 44 D. pore. This structure forebody in all is of little I. GIBSON & R. A. BRAY systematic importance as it occurs mid-ventrally in the anterior hemiuroids. Hermaphroditic duct a duct commonly linking the terminal male and female ducts with the The duct itself appears to have arisen partly as a modification of the genital atrium atrium. genital and partly from the fusion of the male and female ducts. It is normally quite distinct from the genital atrium; but, in certain cases, when the sinus-sac and sinus-organ are absent, it is difficult to distinguish these structures. An hermaphroditic duct occurs in most hemiuroids, commonly within the sinus-sac and almost always within the sinus-organ, when the latter structure is present. Annular muscles are sometimes clearly seen in its walls, e.g. Elytrophalloides, and probably serve to transport eggs and spermatozoa along its length by peristalsis. In some genera, such as Paradinurus and Hemiurus, the proximal part of the hermaphroditic duct is lined by villous, glandular cells of unknown function: this region may serve a similar function to the prostatic vesicle (q.v.) of the lecithochiriines. The distal part of the hermaphroditic duct in Hemiurus is lined with cuticular papillate structures: as this is the region which forms the outer surface of the temporary sinus-organ, it presumably aids the maintenance of the union during copulation. There are indications in Halipegus that the hermaphroditic duct in some species of this genus may be transitory, developing from the sinus-organ as it extends. The absence of an hermaphroditic duct, except in the case of the Hirudinellidae and in Halipegus, is of generic importance only, because of: (1) the inability to distinguish it in some cases from the genital atrium and (2) the fact that degeneration of the terminal genitalia, due to the increasing importance of self-insemination, appears to have occurred independently on a number of ; occasions. Hermaphroditic sac see sinus sac. is the name given by Juel (1889) to the sac-like structure (Fig. 3), filled with active and/or disintegrating spermatozoa found within the structure which we have called Juel's organ (q.v.). In the rudimentary form of Juel's organ (see rudimentary Juel's organ) this sac-like structure has not been enveloped, and is referred to here as a 'rudimentary seminal receptacle' (q.v.). According to Juel (1889) and Lander (1904), the inner vesicle normally appears to have an Inner vesicle- this its distal end, and presumably it is through this that the disintegrating spermatozoa and vitelline material pass into the outer, amorphous mass of Juel's organ. The inner vesicle, which may be oval or in the form of a convoluted tube, appears to act, therefore, as a 'killing chamber' for the excess reproductive material. This structure is present in all of the groups where a fully developed Juel's organ occurs, and its taxonomic significance is as discussed for the latter organ. It should be noted that in the case of certain didymozooids the inner vesicle does not appear to be entirely enveloped by the outer mass of Juel's organ. aperture at JueVs organ - in many hemiuroids, and all hemiurids, Laurer's canal does not open dorsally, but leads into an organ which has been referred to as a 'seminal receptacle' or, more recently 'the pouch of Laurer's canal' (Madhavi & Rao, 1974). It was apparently first described by Juel (1889), and we, therefore, felt (Gibson & Bray, 1975) that Juel's organ was an appropriate designation. It consists of an oval or globular sac containing an amorphous granular material, with the A & embedded in it (Figs 3 4A). An 'inner vesicle' (q.v.), either within this mass and contains spent (but often active) or partly disintegrated spermatozoa, vitelline material and, occasionally, ova. The inner vesicle is fed by Laurer's canal, which may be long or short, depending upon the proximity of Juel's organ to occasional (?) amoeboid cells globular and/or tubular, lies The other end of the inner vesicle opens into the outer mass of Juel's organ. organ and Mehlis' gland are apparently enclosed by a common membranous sheath, but in other species Juel's organ lies outside the sheath surrounding Mehlis' gland. The function of Juel's organ is, apparently, as a disposal unit for excess reproductive material, which enables these resources to be recycled and is thus economically advantageous to the worm compared with the situation where Laurer's canal acts as a drain for these products. It is possible Mehlis' gland. Sometimes Juel's Jo B Fig. 3 [iv, Diagrammatic representation of a fully developed (A) and a rudimentary (B) Juel's organ, 'inner vesicle'; Jo, Juel's organ; Lc, Laurer's canal; rJo, rudimentary Juel's organ; rsr, seminal 46 D. that the (?) down amoeboid cells in the of this waste material. A I. GIBSON & R. A. BRAY outer mass of Juel's organ might be involved in the final break- fully developed Juel's organ is found in all hemiurids (sensu aphanurine bunocotylids, the dictysarcids, the hysterolecithine lecithasterids and in some halipegine derogenid genera. It also occurs, in a slightly modified form, in the nematobothriine didymozooids. In certain derogenine and sclerodistomid genera Juel's organ possesses no inner vesicle. This form, which we consider to be more primitive, we have referred to as a 'rudimentary Juel's organ' (q.v.). In this case there is usually a rudimentary seminal receptacle (q.v.), from which the 'inner vesicle' is later formed, that leads via a region of Laurer's canal of varying length into an amorphous mass, resembling the outer region of the fully developed Juel's organ (Figs 3B & 4B). The presence of a fully developed Juel's organ we consider to be a feature of significance at the subfamily level, except in the case of the Halipeginae, where it is of generic importance stricto), the only (but see Genarchopsis). Laurer's canal -a. duct which links the oviduct with either the exterior, a seminal receptacle (q.v.) or with Juel's organ (q.v.). Its function has long been a matter of contention. Looss (1893) wrote a paper entitled, '1st der Laurers'che Kanal der Trematoden eine Vagina?' and he, Goto (1893) and Johnston (1912) believed that it functioned as a 'sperm-drain'. Cohn (1902, 1903) and Palombi (1931), however, have described examples where Laurer's canal is used as a vagina. This work led Hyman (1951) to state, 'Laurer's canal in flukes was formerly considered to serve as an exit for superfluous sperm and yolk cells but is now known to function in copulation'. Our recent work (Gibson & Bray, 1975) with hemiuroids has indicated that Laurer's canal does in fact function in this group as a drain for excess and/or spent seminal and vitelline material, and we suggest that in other groups the use of this canal as a vagina during copulation is a more recent development associated with the loss of a uterine seminal receptacle (q.v.) and the development of a functional seminal receptacle as a proximal dilation of this canal, i.e. a canalicular seminal receptacle (q.v.). It should be noted that Juel's organ appears to be a modification of Laurer's canal. The nature of Laurer's canal and its presence or absence are often useful features at the subfamily or family level, except in the cases of the Derogeninae, Halipeginae, Prosorchiinae and Trifoliovariinae. Manner's organ (accessory excretory organ or vesicle) - a tubular vesicle lined with an epithelium and usually surrounded by bundles of muscle, especially longitudinal muscle. It occurs dorsal to the excretory vesicle (q.v.) into which it opens postero-ventrally close to the excretory pore. It is a feature of the Scerodistomidae, occurring singly in Prosogonotrema, Prosorchis and Prosorchiopsis and paired in Sclerodistomum. Gibson & Bray (1977) suggest that it might occur in Distoma gigas Nardo, 1827, a giant digenean of uncertain systematic position. The name Manter's organ appears to have been coined by Yamaguti (1971), and is in our opinion more acceptable than the appellation 'accessory excretory organ (vesicle)', as the function of this organ is unknown. Mehlis' gland- a cluster of gland-cells which surround the region of the ovovitelline canal which and the uterus: this is usually the region of the ootype (q.v.). It is thought to produce a mucous secretion which lubricates the uterus and a lipoprotein secretion which forms a membrane around the ovum and vitelline cells upon which shell-material is then deposited links the oviduct (Smyth, 1966). It also seems likely that it may produce a secretion which activates the spermatozoa. Mehlis' gland appears to be of little systematic importance, except that, although in the majority of hemiuroids it is post-ovarian [the oviduct leaves the ovary posteriorly], in the azygiids and accacoeliine accacoeliids it is pre-ovarian [the oviduct leaves the ovary anteriorly]. It is likely that there are several exceptions to this rule, such as the prosorchiine sclerodistomids. In certain hemiuroids Mehlis' gland appears to be enclosed along with Juel's organ by a membranous sac (see Madhavi & Rao, 1974). Melralerm - a name given to the terminal region of the uterus, when it can be distinguished morphologically from the rest of this organ. It is of little taxonomic importance in this group, as it is usually difficult to distinguish and often tends to grade into the uterus-proper. It is usually THE HEMIUROIDEA 47 01 rsr Lc rs rJo 4 Sections of a fully developed (A) and a rudimentary (B) Juel's organ, [gc, gut-caeca; iv, inner organ; Lc, Laurer's canal; Mg, Mehlis' gland; o, ovary; rJo, rudimentary Juel's organ; rs, ventral sucker; rsr, rudimentary seminal receptacle; u, uterus; usr, uterine seminal Fig. vesicle; Jo, Juel's receptacle; v, vitellarium]. 3 3 48 D. I. GIBSON & R. A. BRAY muscular, often surrounded by small gland-cells and in some dinurines it has a villous lining. In Erilepturus (= Uterovesiculurus) it appears to form a distinct dilate sac. -a region of the female duct (ovovitelline canal) where egg-formation and possibly This is normally the region, surrounded by Mehlis' gland (q.v.), which links the oviduct with the uterus. In the hemiuroids this region does not appear to be vesicular as in many other digeneans, but is present as a narrow tube. Although we have seen soft egg-shells in this region in Isoparorchis, Otodistomum and some hemiurids, in othe'rs, such as Derogenes, Pulmovermis and Syncoelium, the ootype appears to extend into the first part of the uterus, as egg-shell formation occurs in a region not surrounded by Mehlis' gland. We are referring to this region as a uterine ootype (q.v.). The systematic significance of these variations of the ootype have not been studied but it seems unlikely that they may be of any value above, perhaps, the generic Ootype fertilization occur. ; level. Ovary - in the hemiuroids this is usually oval in shape, but in certain groups, such as the lecithas- and dictysarcids, it is commonly composed of 4 or 5 distinct lobes. In one instance the ovary is tubular. The position of the ovary in relation to the testes is an impor(Isoparorchis) tant systematic criterion at the subfamily level, except in the case of some of the macrodeninine terids, syncoeliids The ovary is post-testicular in most groups, but is pre-testicular in the azygiine azygiids, the ptychogonimids, the gonocercine derogenids and certain macradeninine lecithasterid genera, and occurs between the testes in the bathycotylids. The ovary occurs in the hindbody in lecithasterids. all groups, except for the prosogonotrematine sclerodistomids. Oviduct - the duct linking the ovary and the ootype (q.v.). It receives Laurer's canal and the vitelline duct before, or sometimes in the case of the common vitelline duct, slightly after entering Mehlis' gland (q.v.). The oviduct appears to leave the ovary posteriorly in the common majority of hemiuroids, the exceptions being the azygiids, the accacoeliine accacoeliids and odd genera, such as Prosorchiopsis, in other groups. possibly Pars prostatica - the region of the male duct between the seminal vesicle and either the ejaculatory duct or the hermaphroditic duct. It is normally surrounded by prostatic gland-cells and lined by what appear to be anuclear gland-cells which often project into the lumen presenting a papillate or villous appearance: it is possible, however, that the latter are merely internal extensions of the outer gland-cells. The function of this region is not known for certain, but it may produce a secretion which protects and lubricates the spermatozoa during ejaculation. It may also be involved in the activation of spermatozoa during ejaculation. The shape of this duct, i.e. whether it is vesicular or tubular, is of specific value, and so is its length. The presence of a vesicular pars prostatica has often been confused with a prostatic vesicle (q.v.). When the external gland-cells are severely restricted in their distribution by surrounding parenchyma or are bound by a fibrous membrane, they are spoken of as being 'delimited'. In certain cases an aglandular duct links the pars prostatica and the seminal vesicle; this is usually referred to as a tubular extension of the seminal vesicle or as an aglandular region of the pars prostatica. An aglandular region also links two parts of the pars prostatica in the dinurine hemiurid Mecoderus. the Peduncle - this is a stalk upon which the ventral sucker may be surmounted. It occurs only in a few species of hemiuroids. It may be of some taxonomic importance at the generic level but it is often variable in size, sometimes being either difficult to distinguish or prominent in the same species, e.g. in Accacladium serpentulum Odhner, 1928, as described by Bray & Gibson (1977). ; Permanent sinus-organ - see sinus-organ (permanent). - regular backwardly directed thickenings of the tegument which surround or partly surround the body transversely. They are a feature unique to the hemiurids and the aphanurine bunocotylids; but only occur in certain genera, being a feature normally considered to be of systematic importance at the generic level (a notable exception being the genus Aphanurus, but see p. 65). They may occur over the whole body (soma) or just part of it, and tend to be better Plications developed anteriorly than posteriorly, especially in the dorsal field. They are never present on the THE HEMIUROIDEA 49 ecsoma. Care should be taken not to confuse these regular tegumental thickenings with a rugate appearance caused by contraction, with small transverse ridges caused by circular muscles in the body-wall of poorly preserved material (these do occur on the ecsoma), and with transverse folds of the body-wall surrounding the suckers of certain bunocotylid genera. Plications appear to be a primitive hemiurid feature which arose in association with the ecsoma (q.v.). They are possibly a feature which permits the thickening of the somatic tegument during periods of low pH or high osmolarity when the ecsoma is withdrawn, and yet still allows full and easy extension and contraction of the body during periods of activity. Certain genera, which possibly no longer inhabit the pyloric region of the stomach or which are parasitic in physiologically 'stomachless' fish (see Barrington, 1957), have lost this feature. Pre-acetabular pit - see presomatic Precaecal sac - see Driisenmagerf pit. ' '. Pre-oral lobe - a small region of the body anterior to the oral sucker. In some instances it may actually overhang the anterior margin of the oral sucker. It has no apparent systematic importance, except that it is glandular in one species of Otodistomum (see Gibson Bray, 1977), as it & appears to occur, at least to some extent, in all hemiuroids. - a deep, concave depression, circular or oval in section, which pit) to the ventral sucker. It occurs in certain lecithochiriine anterior just present mid-ventrally genera, in the plerurine genus Synaptobothrium and apparently in the aphanurine genus Presomatic pit (preacetabular is Mitrostoma. Great care should be taken in its use as a taxonomic criterion as it is easily confused with the ventro-cervical groove (q.v.), which is common in many hemiurids. In the genus Lecithochirium this structure can be either present or absent, being very small and difficult to distinguish in the type-species: this does not appear, therefore, to be a useful character in distinguishing Lecithochirium and Sterrhurus (see p. 93). The presomatic pit often has a region of glandular tissue around but its actual funcits base not understood. Lloyd (1938) has suggested that it acts as a chemo-sensory organ and that it may be associated with the extrusion and withdrawal of the ecsoma it would appear that the latter certainly cannot be the case in Mitrostoma. tion ; is : Prostatic sac prostatica -a term coined by Gibson (1976) for the muscular sac which surrounds the pars vesicle of the azygiids. Its function is not known for certain, but aids the evacuation of spermatozoa and prostatic secretion during ejaculation. and the seminal presumably it Prostatic vesicle - a dilation of the ejaculatory duct within the sinus-sac, which is usually lined by glandular cells and occurs in addition to an external pars prostatica. Essentially, it is identical to an ejaculatory vesicle (q.v.), except for the presence of the glandular cells. As the latter cells can apparently be lost, it does seem unwise to distinguish a prostatic vesicle from an ejaculatory vesicle, and, in view of the possibility of confusing the former structure, both nomenclaturally and morphologically, with a 'vesicular pars prostatica' (q.v.), it might be advisable to refer to the prostatic vesicle as being a 'glandular ejaculatory vesicle'. This structure occurs for certain only in the lecithochiriine, glomericirrine and hypohepaticoline genera, and is possibly a feature of importance at the subfamily level (if included as a type of ejaculatory vesicle). We do not consider that this structure occurs in any of the plerurine or pulmovermine genera, for in these cases the pars prostatica itself appears to be partly enclosed by the sinus-sac in cases when the latter is present. The function of a prostatic vesicle is probably identical to that suggested for an ejacula- tory vesicle. Receptaculum seminis - see seminal receptacle. Receptaculum seminis uterinum see uterine seminal receptacle. Rudimentary Juel's organ - a form of Juel's organ (q.v.) which lacks an 'inner vesicle' (q.v.). It has a granular appearance and is present usually at the distal end (Figs 3B & 4B), but occasionally more proximally, of Laurer's canal. It presumably has a similar function to a fully developed Juel's organ, into which it has probably evolved in more advanced forms by enveloping the D. 50 I. GIBSON & R. A. BRAY rudimentary seminal receptacle (q.v.) and forming an 'inner vesicle'. Small, black structures can be seen within the amorphous mass which fills this organ: we wonder whether these might be bacteria which may carry out the final breakdown of the excess seminal and vitelline material, much we amoeboid might do in a fully developed Juel's organ. and prosogonotrematine and prosorchiine sclerodistomid genera, but its taxonomic significance, even at the generic level, is uncertain. This organ also appears to occur in the aspidogastrean Aspidogaster conchicola von Baer, 1826 (see p. 123). as suggest that (?) A rudimentary Juel's organ Scales We -a is known cells to occur in certain derogenine derogenid term used by Manter (1934) to describe the structures on the tegument of Dinosoma. believe that they are probably just regularly crenulate plications (q.v.). Seminal receptacle - a general term covering several different types of apparatus for the storage of spermatozoa in the female reproductive system. In our opinion the various forms of seminal receptacle should be clearly differentiated in descriptions, as they are important taxonomic We recognize four different kinds of seminal receptacle present in the Hemiuroidea a 'blind seminal receptacle' (q.v.), which is a blind sac, linked to the oviduct by a (Fig. short tube, occurring in most of the lecithasterid subfamilies, the opisthadenine bunocotylids and the derogenid genus Leurodera, and which appears to have evolved from Juel's organ (q.v.) or in some cases from a rudimentary or canalicular seminal receptacle; (2) a 'canalicular seminal receptacle' (q.v.), which is a large proximal dilation of Laurer's canal, and occurs frequently in other groups of digeneans, but apparently within the Hemiuroidea it occurs for certain only in the lecithasterid genus Trifoliovarium and in a modified form in the derogenid genus Progonus; (3) a 'rudimentary seminal receptacle' (q.v.), which is a small proximal dilation of Laurer's canal that, when present, always occurs together with a uterine seminal receptacle, but this form differs from the others in that it is not a store of fresh, quiescent spermatozoa and in that the small amount of spermatozoa which it does contain are spent, although often still active; and (4) a criteria. 1): (1) 'uterine seminal receptacle' (q.v.), which is a store of spermatozoa present in the proximal region of the uterus, and occurs in the majority of hemiuroids. Another type is an 'oviducal seminal receptacle', which is formed as a dilation of the oviduct; but this type does not occur in the Hemiuroidea. With the exception the 'rudimentary' and 'uterine' types, the various forms of seminal receptacle do not normally occur together in the same individual. Seminal sac - a term used by Manter (1947) for an oval, muscular sac which encloses a convoluted, tubular seminal vesicle in the bunocotylid Opisthadena dimidia Linton, 1910. It appears to be a modification of the muscular type of seminal vesicle where the muscular wall is clearly not associated with the membranous lining of the seminal vesicle. It also occurs in some of the other species of Opisthadena and in the hemiurid Elytrophalloides. - a dilation of the vas deferens (q.v.) which forms a store of spermatozoa which It is often provided with a muscular wall or with sphincter muscles which constrict it into portions. These modifications, which are often of systematic importance at the generic level, are involved with the evacuation of spermatozoa from the seminal vesicle, through Seminal is vesicle ready for ejaculation. the pars prostatica and into the hermaphroditic duct, often against the hydrostatic pressure produced by the sinus-sac (q.v.). The shape of the seminal vesicle is also often of specific or generic value, as is its position in relation to the ventral sucker. In the more primitive forms it is usually tubular. In the hemiuroids the seminal vesicle is normally free in the parenchyma, but in certain halipegine derogenids it may be partly or completely enclosed within the sinus-sac., in the azygiids contained within a prostatic sac (q.v.), and in certain species of Opisthadena it forms a it is 'seminal sac' (q.v.). Sinus-organ (permanent) -a copulatory organ of variable from the wall of the normally well-developed phroditic duct. This type of sinus-organ cone when completely retracted. forms are sometimes found (Fig. It 5): is size which is usually formed externally and internally from the herma- genital atrium contractile, but is still visible in sections as a small usually occurs in one of two forms, although intermediate B tso The types of sinus-organ Fig. 5 B. Amuscular sinus-organ; C. occurring in the Hemiuroidea: Temporary sinus-organ, tso, temporary sinus-organ.] [so, A. Muscular sinus-organ; permanent sinus-organ; ss, sinus-sac; 52 D. I. GIBSON & R. A. BRAY - where it is probably everted (1) 'Muscular' entirely or partly by its own intrinsic musculature (when partly, the remaining force is supplied by hydrostatic pressure produced by the sinus-sac: see Gibson & Bray, 1974): this form occurs in many of the more primitive hemiuroid groups (see p. 129); 'Amuscular'* - a form, associated with the presence of a thick-walled (muscular) seminal vesicle, which is probably everted entirely, or almost entirely, by hydrostatic pressure produced (2) by the sinus-sac upon its contents: this form occurs in the elytrophalline and glomericirrine hemiurids, the muscular seminal vesicle being required to force spermatozoa into the hermaphroditic duct against the hydrostatic pressure built up by the walls of the sinus-sac. The presence or absence and type of sinus-organ are often useful taxonomic criteria up to the subfamily level; but the sectioning of specimens is essential and great caution must be exercised in the use of this feature. See sinus-organ (temporary). - an amuscular or Sinus-organ (temporary) weakly muscled copulatory organ, formed from the hermaphroditic duct by hydrostatic pressure within the sinus-sac, which is a transitory structure (Fig. 5). It is usually only present during copulation, but also occurs occasionally in fixed specimens. The genital atrium is usually small or apparently absent in forms with a temporary sinusorgan. Naturally 'permanent' [see sinus-organ (permanent)] and 'temporary' types of sinus-organ cannot occur in the same species of worm. The two forms, however, may be difficult to distinguish when only a small number of specimens is available for study. A temporary sinus-organ may be associated with slight thickenings in the wall of the seminal vesicle, but is more often associated with the presence of sphincter muscles which tend to partition the seminal vesicle and are capable of exerting pressure, thus forcing spermatozoa into the sinus-sac against its internal hydrostatic pressure during ejaculation. As the genital atrium tends to be short or absent, the temporary sinus-organ itself is also short, and, therefore, the hydrostatic pressure required to extrude it is reduced. The sinus-sac tends, therefore, to be smaller than in forms with an amuscular permanent sinus-organ. lids and A temporary sinus-organ occurs in the more advanced forms of hemiurids, bunocoty- lecithasterids. As this transitory structure is rarely seen everted, it is of no systematic significance. Sinus-sac or hermaphroditic sac - a muscular sac which surrounds the base of the genital atrium, if present, and encloses the hermaphroditic duct and/or the terminal portions of the ejaculatory duct and uterus. Its apparent function is to aid the eversion of a permanent sinus-organ (q.v.) or the production of a temporary sinus-organ (q.v.) from the hermaphroditic duct. It may also aid the expulsion of spermatozoa and eggs, especially the former in cases where an ejaculatory (or prostatic) vesicle (q.v.) or the seminal vesicle is enclosed within the sinus-sac. In certain instances, some of the plerurine hemiurids, there may be a large proximal gap in the wall of the sinus-sac at the point through which the male and female ducts pass: this is known as an 'opentype' of sinus-sac and is probably a vestigial form. In other groups of hemiuroids the sinus-sac e.g. in may be reduced, or in some cases completely lost. Sectioning is essential when the sinus-sac is apparently absent, as the vestiges of this structure are often insignificant. This feature is frequently of some importance at the family level, as it is missing in the Azygiidae and Hirudinellidae, which possess a 'prostatic sac' (q.v.) and a 'cirrus-sac' (q.v.), respectively; but great care should be exercised in the utilization of this feature, as it appears to have been lost independently in certain genera from a number of distantly related hemiuroid groups, e.g. Gonocerca, Syncoelium, Tetrochetus, Prolecitha and Bunocotyle. Temporary sinus-organ - see sinus-organ (temporary). Testes - there are usually two globular testes present in hemiuroids. Exceptions are the syncoeliids, which either have a much larger number (11-18) of large oval masses (referred to as testes, although there are only two vasa erTerentia) or possess apparently follicular testes, and two lecithasterid genera, Monorchiaponurus and Monorchimacradena, which are reported to have one testis. * Presumably there are some longitudinal muscle fibres present which permit contraction of this type of sinus-organ. THE HEMIUROIDEA An important feature at the subfamily level (except in 53 some members of the Macradenininae) ovary usually being post-testicular. In the gonocercine derogenids and certain macradeninine ptychogonimids, the relationship between the ovary the azygiine azygiids, the is and the testes, the however, it is pretesticular, and in the bathycotylids it is inter-testicular. The relative positions of the testes and their shape are of little value above the specific level, except that in the dictysarcid genus Elongoparorchis they do appear to be consistently The lecithasterids, elongate. testes normally occur in the hindbody, except in the prosogonotrematine and prosorchiine sclerodistomids. Uroproct the aperture of the excretory vesicle when the base of the latter organ communicates directly with the distal extremities of the gut-caeca. uroproct, therefore, serves as an orifice for the evacuation of waste-products from both the excretory and alimentary systems. This structure occurs independently and regularly in the Accacoeliidae, Hirudinellidae, Ptychogonimidae and A Otiotrematinae, but, except for the Accacoeliinae and the Ptychogonimidae, it does not occur in of the genera in these groups. It is normally considered to be a feature of generic importance. all Uterine ootype - the proximal region of the uterus, present in some species, into which the region of egg-formation extends. Its systematic importance is not understood. See ootype. Uterine seminal receptacle or receptaculum seminis uterinum - a term given to the proximal region of the uterus when it is filled with 'fresh' spermatozoa and is, therefore, acting as a seminal store This region can normally only be differentiated from the remainder of the uterus by the presence of spermatozoa. It is the commonest form of seminal receptacle (q.v.) present in the Hemiuroidea, being absent only in the lecithasterids (with the exception of the Hysterolecithinae), (Fig. 1). the opisthadenine bunocotylids and in the derogenids Progonus and Leurodera. This type of seminal receptacle is probably associated with cross-insemination, using the genital atrium as a vagina, or with self-insemination, and differs from all other types of seminal receptacle in that spermatozoa pass towards the ovary through the ootype. In the past many workers have mistaken a canalicular seminal receptacle (q.v.), but in sectioned material the two can be distinguished. Except in the cases of the derogenids Progonus and Leurodera, the presence or absence of this type of seminal receptacle is an important systematic feature at the subfamily level. Great care must be exercised with the use of this feature because it is by nature transitory, and, when empty, it is not recognizable as a seminal store. We have observed, in sectioned material, specimens of Hirudinella and Prosorchiopsis (forms possessing a uterine seminal receptacle) which do not have any spermatozoa in the proximal region of the uterus. this structure for easily Uterus - a duct, normally full of eggs, which links the ootype with the hermaphroditic duct, genital atrium or genital pore. The distal extremity may be modified to a form metraterm (q.v.), and the proximal extremity may form a uterine seminal receptacle (q.v.) or a uterine ootype (q.v.). In addition to transporting eggs, the proximal region of the uterus appears to be involved in the hardening and tanning of the egg-shells. The uterus often coils between the ovary and the ventral sucker, but it may loop well posterior to the ovary and in some cases coils in the forebody. Its distribution tends to be of generic importance and occasionally of subfamilial importance, especially in cases where it reaches into the post-ovarian field or is entirely pre-ovarian. Vasa efferentia - single narrow ducts which connect each testis with the vas deferens (q.v.). In the Syncoeliinae, where there are 11-18 so-called testes, there are the usual two vasa efferentia, and the ducts linking these testes to the vasa efferentia are called 'collecting ducts'. The vasa efferentia are of no apparent systematic importance in the Hemiuroidea. Vas deferens - a duct formed by the fusion of the two vasa efferentia (q.v.), which, in almost all cases, is dilate, filled with spermatozoa and referred to as the seminal vesicle (q.v.). In itself, therefore, it is of no systematic importance, although in certain groups there is a narrow duct linking the seminal vesicle with the pars prostatica (q.v.). Ventro-cervical groove - a transverse crevice which occurs anterior to the ventral sucker in many hemiurids. It on the ventral surface immediately appears to have no actual function, as it is 54 D. GIBSON & I. R. A. BRAY simply caused by the close proximity of the oral and ventral suckers in some of these genera. The size of this feature appears to be dependent upon the degree of contraction which occurs in the forebody during fixation. It appears to have no systematic value, except that been mistaken for a presomatic pit (q.v.). it has occasionally Vitellarium - a structure of variable accompany the ovum morphology that produces vitelline (yolk) cells which The form of the vitellarium is a valuable taxonomic the family level. The common arrangements of the vitellarium in egg-formation. criterion ranging from the species to in the Hemiuroidea are as follows (see Fig. 7): (1) follicular; (2) linked follicles, giving a chainlike tubular arrangement; (3) convoluted tubules which are often branched; (4) about seven tubules, usually arranged four on one side of the body and three on the other; (5) about seven oval to digitiform lobes; (6) two oval or slightly lobed masses; and (7) a single oval mass. These forms tend to grade into one another, but it is noticeable that the seven-lobed vitellarium occurs widely throughout the group. The arrangement of the vitellarium is discussed in more detail on p. 124. One unusual feature occurs in the Accacoeliinae, where the sinistral side of the system is reduced to a vestige. In certain instances, especially in the Lecithasteridae and the Derogenidae, the relationship between the vitellarium and the ovary is useful systematically; but the vitellarium or at least the origin of the main vitelline ducts is usually post-ovarian, although exceptions to this include the azygiids and the accacoeliine accacoeliids. III. A classification of the Hemiuroidea with keys and definitions Introduction The following classification, which we propose for the Hemiuroidea, is based upon adult morphology associated with an attempt to understand the function of the organs and organ-systems (see p. 39). This relies heavily upon comparative morphology, as do most of the previous classifications. The main problem with this, as discussed above, is that much of the descriptive work over the years has been inadequate. Many workers around the turn of the century gave detailed and careful descriptions, based upon sectioned material. Work of this standard has been the exception, rather than the rule, since that time. In attempting to provide a feasible classification we have, therefore, examined as many species as possible, both in serial sections and wholemounts. The lack of certain material has left large gaps, which have had to be filled with a critical appraisal of the literature. In certain groups, and in particular in many individual genera, much of the detail necessary to classify the animals has not been supplied by the original authors. In these cases our classification is particularly tentative, and we have usually indicated where we consider our knowledge to be totally inadequate. In some instances, using our knowledge of the groups as a whole and assessing the functional requirements present, we have assumed the morphology of certain undescribed or apparently wrongly interpreted structures. While this may seem somewhat unsatisfactory, some of our interpretations were proved correct during the course of the work, e.g. before specimens were obtained we correctly assumed the presence of a sinus-sac, rather than a cirrus-sac, in Arnold and Glomericirrus, and we correctly assumed the presence of Juel's organ in Elongopat-orchis and in many of the hemiurids (sensu stricto). As far as the systematics of this group is concerned, we have faced many problems in weighing the relative values of different factors. At one time we were inclined to give considerable weight to the details of the terminal genitalia, and also to the vitellarium. While these factors may have significance at the generic or subfamily level, they do seem to be susceptible to development or regression in certain groups. The details of the proximal region of the female system have, we believe, a fundamental value in distinguishing subfamilies, although there are exceptions to this, for in the Derogenidae and the Trifoliovariinae a variety of conditions occur. The presence of Juel's organ, for example, seems to be of considerable importance; but, even in this case, care has to be taken, and the complete morphological pattern must be taken into consideration. Definitions of the taxa are presented ; but features common to a group of taxa are given in the definition of the higher taxa, rather than repeated throughout the group. Features, especially THE HEMIUROIDEA those taken from the literature, which we 55 believe to be questionable, are indicated by question- marks. Wherever possible material was examined, especially in serial section. The abbreviations used what material we have seen are given after the generic name, and are as follows: T=type-material of type-species; t=non-type material of type-species n=material of non-typeto indicate ; species; w=whole-mount; s=serial sections. The absence of this information indicates that the data have been derived from the literature. We have attempted to provide dichotomous keys to the taxa. Rather than relying upon the most obvious of criteria, we have tried to produce keys which work, with the result that the sectioning of material, while always advisable, may in fact be essential. These keys must be used with care, and with the understanding that this classification is based upon polythetic assemblages of characters. Soft-bodied animals, such as digeneans, give few good metrical or meristic characso that it is very important to possess a good understanding of the overall morphology while ters, attempting to determine these worms. Some readers may note that the authorities which we have given for some of the familygroup names differ from those presented by some other workers. These workers appear to have followed a recent trend which tends to confuse systematics and nomenclature. In using the authority for the original mention of the family-group name, irrespective of suffix, we are following Article 36 of the International Code of Zoological Nomenclature. As with any work of this kind, our classification must be considered provisional. We hope that it may be helpful in stimulating and encouraging a closer and more careful examination of the worms in this group. Superfamily HEMIUROIDEA Looss, 1899 Azygioidea Liihe, 1909 Accacoelioidea Odhner, 1911 Isoparorchioidea Travassos, 1922 Body small to large; oval to cylindrical. Ecsoma present or absent. Body-surface smooth, rugate or plicated (or 'scaley'); never spiny, but occasionally papillate. Oral and ventral suckers well developed, occasionally small. Ventral sucker normally in middle or anterior half of body, occasionally just inside posterior half of body; occasionally pedunculate. Prepharynx absent. Pharynx well developed; normally oval, occasionally modified. Oesophagus usually short, occasionally long. 'Driisenmagen' present or absent. Gut-caeca usually end blindly near posterior extremity, occasionally form cyclocoel or uroproct. Testes normally two, rarely one or follicular; normally tandem to symmetrical, preovarian and near middle of body; occasionally in forebody or post-ovarian. Seminal vesicle oval to tubular; occasionally constricted into portions usually thin- but occasionally thick-walled; in fore- or hindbody; normally external to sinus-sac, rarely partly or entirely internal. Pars prostatica tubular to vesicular; long or short; normally external to sinus-sac, rarely internal; usually in forebody, occasionally entirely inside, or extending into, hindbody. Ejaculatory duct usually present; usually short; often within sinus-sac or sinus-organ; normally unites with metraterm to form hermaphroditic duct; occasionally within 'cirrus-sac'. Hermaphroditic duct usually present; usually within sinus-sac and/or sinus-organ. Sinus-sac present or absent; oval to cylindrical; normally enclosing ejaculatory duct and part of metraterm and/or hermaphroditic duct; occasionally additionally enclosing ejaculatory (prostatic) vesicle or seminal vesicle and/or pars prostatica. Permanent sinus-organ present or absent within genital atrium; conical to tubular; muscular or non-muscular. Temporary sinus-organ sometimes formed from hermaphroditic duct. 'Cirrus-sac', enclosing ejaculatory duct only, and 'cirrus' rarely present. Genital atrium large, small or absent. Common genital pore mid-ventral in forebody. Ovary usually oval, occasionally lobed, rarely tubular or follicular; usually post-testicular, occasionally pre-testicular, rarely inter-testicular; normally in hindbody, rarely in forebody. Mehlis' gland usually post-ovarian, occasionally pre-ovarian. Uterine seminal receptacle plus Laurer's canal and/or Juel's organ or blind seminal receptacle alone normally present. Uterine much of hindbody, occasionally extending well into forebody, rarely entirely in forebody. Eggs normally oval; usually small, numerous; occasionally with spine, filament(s) or coils usually fill 56 D. GIBSON & I. BRAY R. A. threads. Vitellarium normally follicular, tubular or composed of a small number (often seven) oval to tubular lobes or one to three (usually two) entire or lobed masses; often post-ovarian, occasionally pre-ovarian; sometimes extending throughout hindbody or into forebody, rarely entirely in forebody. Excretory pore terminal; vesicle Y-shaped; arms united in forebody or not. Manter's organ (accessory excretory vesicle) rarely present. Parasitic in gut, especially stomach, primarily of marine teleosts, but commonly occur in freshwater teleosts and elasmobranchs, occasionally in holosteans, amphibians, reptiles and progenetic in invertebrates; occasionally recorded from gills, skin, body-cavity, swim-bladder and other organs. Key 1. 2. to Hemiuroidea A. Vitellarium ..... B. composed of numerous widely distributed follicles Vitellarium otherwise, usually composed of a small number of oval to tubular (occasionally branched) lobes or 1-3 distinct oval, lobed or unlobed masses A. Prostatic sac present; parasitic in elasmobranchs B. Prostatic sac absent; parasitic in gut of elasmobranchs Testes 2, occasionally 1 and freshwater .... A. PTYCHOGONIMIDAE (p. . Testes follicular, 11-18 large or many small follicles arranged in rows or irregularly distributed; usually parasitic in buccal or branchial cavities or on skin (? occasionally A. Ecsoma absent (take care with this observation as some hemiurids have a reduced ecsoma and some bunocotylids may retain the vestige of an ecsoma) Ecsoma present (sometimes very reduced); body surface often plicated; Juel's organ and A. B. elasmobranchs and marine teleosts . . . SYNCOELIIDAE (p. 114) ..... A. B. 7. A. B. ...... Ovary oval or lobed Ovary tubular; parasitic ............ ........... (p. 62) (7) swim-bladder of freshwater teleosts ISOPARORCHIIDAE (p. 100) Ventral sucker anterior to middle of body; parasitic in marine teleosts; seminal vesicle in never enclosed in sinus-sac Ventral sucker usually in or near middle of body, occasionally more anterior; significant proportion of uterus usually present in forebody [a small number of marine forms do possess a ventral sucker in the anterior half of the body and uterine coils which do not extend into the forebody, but these forms also possess a seminal vesicle which is enclosed within the sinus-sac]; vitellarium 1 or 2 masses, entire or lobed (lobes normally shallow, rarely digitate); seminal vesicle in forebody; ovary and vitellarium pre- or posttesticular; parasitic mainly in gut of freshwater and marine teleosts, occasionally in .... 8. (5) uterine seminal receptacle present; vitellarium varies between form with 7 tubular lobes and form with 2 distinct oval masses; parasitic mainly in gut of marine teleosts, HEMIURIDAE (p. 84) occasionally present in freshwater teleosts and lung of sea-snakes Ovary usually post-testicular, occasionally pre-testicular (6) Ovary inter-testicular; parasitic on gills (? and in stomach) of marine teleosts BATHYCOTYLIDAE 6. 110) (4) B. B. 5. (p. 60) ............ internally) of 4. (3) teleosts AZYGIIDAE 3. (2) A. amphibians, reptiles and freshwater shrimps 'Cirrus' present, enclosed in 'cirrus-sac'; female duct B. ally present in salmonids) 'Cirrus' and 'cirrus-sac' absent dently; large parasites from gut ( or ? gills) DEROGENIDAE (8) (p. 71) opens into genital atrium indepenof marine teleosts (immature forms occasion- HIRUDINELLIDAE (p. 98) 9. A. 10. A. male and female ducts normally unite forming hermaphroditic duct, which is often present within a sinus-organ and enclosed by a sinus-sac (9) Parasitic in gut (occasionally on gills) (10) Parasitic in swim-bladder or gall-bladder (13) BUNOCOTYLIDAE (p. 62) Vitellarium 1, 2 or 3 compact masses B. Vitellarium otherwise A. Vitellarium 6-8 (occasionally twice this number) oval to digitiform lobes, often arranged in rosette, occasionally branched Manter's organ absent pharynx oval ; ........ .... . B. 1 1. . . . . . . . . ; 12. . . . . . (11) ; .... LECITHASTERIDAE (p. 101) B. Vitellarium tubular (filamentous) A. SCLERODISTOMIDAE (p. Ill) Manter's organ present; pharynx oval Manter's organ absent; pharynx with narrow anterior extension into base of oral sucker; occasionally present on gills; commonly parasitic in sunfish (Molidae) B. (12) ACCACOEL1IDAE (p. 57) THE HEMIUROIDEA 13. 57 .... Parasitic in swim-bladder; vitellarium 6-8 oval to digitiform lobes, 2 A. late masses or 2 acinous groups of follicles compact multilobu- DICTYSARCIDAE Parasitic in gall-bladder; vitellarium tubular, dendritic, with anteriorly oriented main collecting ducts situated medially B. SCLERODISTOMOIDIDAE (p. . Family ACCACOELIIDAE (p. 81) and posteriorly 114) Odhner, 1911 elongate. Ecsoma absent. Body-surface smooth, but forebody and ventral suckers well developed. Ventral sucker normally in anterior half of body; may be pedunculate. Pharynx well developed; with narrow anterior extension into base of oral sucker; occasionally modified posteriorly. Oesophagus usually long, occasionally short. 'Driisenmagen' present. Gut-caeca usually H-shaped; terminate blindly or more commonly form uroproct. Testes two; oblique or in tandem; in hindbody, normally close to middle of body; Body large or small, may be commonly papillate. Oral pre-ovarian. Seminal vesicle thin-walled; tubular; sinuous or convoluted; commonly reaching into hindbody. Pars prostatica tubular; external gland-cells may be delimited. Short ejaculatory present within sinus-sac. Hermaphroditic duct present or absent. Sinus-sac and sinus-organ present or absent. Genital atrium present. Ovary oval post-testicular. Mehlis' gland pre- or post-ovarian linked to anterior or posterior region of ovary by oviduct. Laurer's canal duct commonly ; ; Juel's organ and canalicular or blind seminal receptacle absent. Uterus extensive; coils entirely or almost entirely in hindbody; usually passes close to and uterine seminal receptacle present. posterior extremity before looping forward again. Eggs numerous; small; non-filamented. Vitellarium with one or two main collecting ducts composed of numerous filamentous tubules (? or occasionally chains of follicles) in various parts of the fore- or hindbody. Excretory vesicle ; Y-shaped arms ; initially in dorsal and ventral fields, united in forebody. Metacercariae usually in on gills of marine teleosts. coelenterates or ctenophores. Parasitic in gut or occasionally COMMENT The vitellarium of the Paraccacladiinae is typical of many of the primitive hemiuroids, a possessing symmetrical pair of main collecting ducts which branch distally and unite proximally to form a common collecting duct. In the Accacoeliinae, however, it appears that the right half of the vitelline system is reduced to a small vestigial process (or reservoir). The whole of the vitelline system of the latter group, therefore, corresponds to only the left-hand side of the vitellarium in other hemiuroids. Key 1. to Accacoeliidae A. Oesophagus long and narrow; gut-caeca H-shaped; uroproct present; Mehlis' gland preovarian, linked to anterior region of ovary by oviduct; vitellarium with single main ACCACOELIINAE (p. 57) collecting duct and system of branching tubules Oesophagus short; gut-caeca not distinctly H-shaped and end blindly; Mehlis' gland postovarian, linked to posterior region of ovary by oviduct; vitellarium with symmetrical PARACCACLADIINAE (p. 59) pair of collecting ducts and system of branching tubules . B. . . Subfamily ACCACOELIINAE Odhner, 1911 Tetrochetinae Looss, 1912, emend. Dollfus, 1935 Accacladiinae Yamaguti, 1958 Orophocotylinae Yamaguti, 1958 Rhynchopharynginae Yamaguti, 1958 Guschanskianinae Skrjabin, 1959 Body usually elongate. Body-surface smooth, but forebody may be papillate. Lateral flanges occasionally present on ventral sucker. Pharynx occasionally modified to form two muscular bulbs (Rhynchopharynx). Oesophagus long and thin. Gut caeca H-shaped. Uroproct present. Sinus-sac and sinus-organ present or absent; sinus-sac well or poorly developed when present. Mehlis' gland pre-ovarian; linked by oviduct to anterior region of ovary. Vitellarium filamentous; with single main collecting duct on right and single system of ramifying branches in fore- or hindbody; left-hand system reduced to small process or small ramifying system. Parasitic on gills or in gut of marine teleosts (especially Molidae). 58 D. Key 1. A. B. 2. I. GIBSON & A. B. A. BRAY Well-defined sinus-sac and sinus-organ present (2) Well-defined sinus-sac and sinus-organ absent (5) Ectoparasitic on gills; long proboscis-like sinus-organ; strongly developed ventral musculature in hindbody; enormous pars prostatica occupying much of forebody; vitellarium ACCACOELIUM posterior to anterior testis Endoparasitic in gut; short cylindrical or dome-shaped sinus-organ; vitellarium not usually extending posteriorly to ovary 3. R. A. ........ ........ to Accacoeliinae ......... .... (3) B. Pharynx pyriform with anterior extension into base of oral sucker Pharynx with two bulbs and anterior elongate portion ensheathed A. process of oral sucker; glandular oesophageal bulb immediately posterior to pharynx; large glandular organ of unknown function at base of peduncle Vitellarium confined to hindbody; ventral sucker on extensible peduncle; pars prostatica in (4) glandular posterior RHYNCHOPHARYNX 4. ACCACLADIUM B. relatively short Vitellarium wholly or partly in forebody; ventral sucker sessile or nearly so; pars prostatica long Diffuse muscular region around metraterm; muscular sucker-like pads on antero-dorsal surface ACCACLADOCOELWM 5. A. ODHNERWM B. 6. A. B. No sinus-sac detectable; no muscular pads present on antero-dorsal surface Vitellarium a tubular branching structure on either side of hindbody; no flange on ventral . sucker Vitellarium comprising (?) few follicles in four rows between the anterior base of the peduncle; small flange on ventral sucker . . ACCACOELIUM Monticelli, . . . (6) TETROCHETUS testis and the OROPHOCOTYLE 1893 [t(w,s)] Forebody papillate. Oesophagus reaches to ventral sucker. Ventral sucker on short peduncle. Thick muscular layer in ventral hindbody. Sinus-sac present surrounding base of genital atrium. Sinus-organ long and strongly muscular, frequently extended through genital pore. Enormous pars prostatica and associated gland-cells occupy much of forebody. Vitellarium posterior to anterior testis. Parasitic on gills of marine teleosts (Mola). TYPE-SPECIES. Accacoelium contortum (Rudolphi, 1819) [by subsequent designation: Looss, 1899]. ACCACLADIUM Odhner, 1928 [t(w,s>] Body-surface smooth. Oesophagus reaches to ventral sucker. Ventral sucker on extensible peduncle. Pars prostatica well developed. Sinus-sac surrounding base of genital atrium. Sinusorgan short, cylindrical. Vitellarium between ventral sucker and ovary. Parasitic in intestine of marine teleosts (Mola). TYPE-SPECIES. Accacladium serpentulus Odhner, 1928 [by original designation]. ACCACLADOCOELWM Odhner, 1928 [t(w,s); n(w,s)] Guschanskiana Skrjabin, 1959 Body smooth. Lateral flanges on ventral sucker present or absent. Oesophagus reaches to ventral sucker. Pars prostatica long. Sinus-sac present surrounding base of genital atrium. Sinus-organ short, cylindrical. Vitellarium reaches anteriorly to oral sucker, may extend posteriorly just past ovary but usually not beyond anterior testis; reduced fraction may branch. Parasitic in intestine of marine teleosts (Mola). TYPE-SPECIES. Accacladocoelium nigroflavum (Rudolphi, 1819) [by original designation]. ODHNERWM Yamaguti, Mneiodhneria Dollfus, 1935 Caballeriana Skrjabin & Guschanskaja, 1959 1934 [t(w,s)] THE HEMIUROIDEA 59 Body-surface smooth, but with muscular sucker-like pads on antero-dorsal surface. Flange-like muscular extensions present on ventral sucker; latter pedunculate. Oesophagus reaches to ventral sucker. Pars prostatica reaches half-way back to ventral sucker. Diffuse muscular region surrounds distal parts of metraterm and genital atrium (may be vestige of sinus-sac). Male duct enters genital atrium from side through small papilla. Vitellarium tubular, extending from pharynx to ovary. Parasitic in intestine of marine teleosts (Mold). TYPE-SPECIES. Odhnerium calyptrocotyle (Monticelli, 1893) [by original designation]. COMMENT. We are using the appellation Odhneria Travassos, Nomenclature. to 1921, in Odhnerium rather than Mneiodhneria, despite its similarity accordance with the International Code of Zoological OROPHOCOTYLE Looss, 1902 [Inadequately described.] Body-surface smooth. Ventral sucker pedunculate; bears small flange. short. Sinus-sac not reported. Sinusorgan absent. Vitellarium reported to consist of few (?) follicles in four rows between testes and ventral sucker. Parasitic in intestine of marine teleosts (Ranzanid). Oesophagus not reaching to ventral sucker. Pars prostatica TYPE-SPECIES. Orophocotyle planci (Stossich, 1899) [by original designation]. : RHYNCHOPHAR YNX Odhner, 1928 [t(w,s)] Forebody papillate. Ventral sucker pedunculate. Pharynx consisting of two muscular bulbs [the 'pharynx-proper' and the 'Russelblase' (snout-bladder)] and an extended anterior snout ('Russel'), which may be extended through the oral sucker. Oral sucker possesses posterior glandular extension, the snout-sheath ('Russelscheide'), which envelopes the snout. Glandular oesophageal bulb present immediately posterior to pharynx. Oesophagus reaches to ventral sucker. Large glandular organ of unknown function present at base of peduncle. Pars prostatica long. Sinussac surrounds base of genital atrium. Sinus-organ small. Vitellarium extends from anterior region of ventral sucker to ovary. Parasitic in intestine of marine teleosts (Mold). TYPE-SPECIES. Rhynchopharynx paradoxa Odhner, 1928 [by original designation]. TETROCHETUS Looss, 1912 [t(w,s) ; n(w,s)] Paratetrochetus Hanson, 1955 Body-surface smooth. Ventral sucker pedunculate. Oesophagus long. Diverticula present at narrow. Sinus-sac and sinus-organ absent. Male and female ducts open together into shallow genital atrium. Vitellarium tubular, in hindbody; reduced half may be branched. Parasitic in intestine of medusophagus and carnivorous marine teleosts. intestinal bifurcation. Pars prostatica short, straight, TYPE-SPECIES. Tetrochetus raynerii (Nardo, 1833) [by monotypy]. Subfamily PARACCACLADIINAE Bray & Gibson, 1977 Body elongate. Body-surface smooth, but with papillae on outer surface of ventral sucker. Ventral sucker on short peduncle. Pharynx extended into base of oral sucker. Oesophagus short, wide. Anterior caecal shoulders small. Gut-caeca terminate blindly near posterior extremity. Pars prostatica elongate, convoluted. Sinus-sac present surrounding base of genital atrium; musculature diffuse. Sinus-organ short, cylindrical. Mehlis' gland post-ovarian; linked to posterior region of ovary by oviduct. Vitellarium with symmetrical pair of main collecting ducts and ramifying systems of tubules; posterior to ovary. Mature forms parasitic in rectum of carnivorous marine teleosts (Coryphaenoides) immature forms parasitic in rectum of medusophagus marine teleosts. ; 60 D. GIBSON & I. R. A. PARACCACLADIUM Bray & BRAY Gibson, 1977 [T(w,s)] Defined as subfamily. TYPE-SPECIES. Paraccacladiwn jamiesoni Bray Family & Gibson, 1977 [by original designation]. AZYGHDAE Liihe, 1909 Aphanhysteridae Guiart, 1938 Body large or small usually elongate. Ecsoma absent. Body-surface smooth, without spines or plications. Oral and ventral suckers well developed ; latter in middle or anterior half of body. Prepharynx absent. Pharynx well developed. Oesophagus usually short. 'Driisenmagen' apparently ; absent. Gut-caeca terminate blindly close to posterior extremity. Testes two; in tandem, oblique or symmetrical; pre- or post-ovarian in hindbody. Seminal vesicle tubular, usually short, thin- walled; convoluted in forebody. Pars prostatica tubular. Prostatic sac present surrounding pars and seminal vesicle. Ejaculatory duct usually long and convoluted, but of variable length. Hermaphroditic duct short; at distal extremity of sinus-organ. Permanent sinus-organ prostatica variable in length; usually conical. Sinus-sac absent. Genital atrium usually well developed; variable in size. Genital pore mid- ventral in forebody. Ovary oval; pre- or post-testicular. Mehlis' gland pre-ovarian. Laurer's canal and uterine seminal receptacle present. Juel's organ and canalicular or blind seminal receptacle absent. Uterus entirely or almost entirely pre-ovarian; coiled mainly in hindbody. Eggs numerous; small; non-filamented. Vitellarium follicular; usually present laterally throughout much of hindbody; occasionally extending into forebody. Excretory Y-shaped arms united in forebody or not. Parasitic in stomach or body-cavity of elasmobranchs and in stomach of freshwater teleosts and holosteans. vesicle Key ; to Azygiidae LA. B. Testes post-ovarian Testes pre-ovarian Subfamily AZYGIINAE AZYGIINAE (p. 60) LEUCERUTHRINAE (p. 62) Liihe, 1909 Aphanhysterinae Guiart, 1938 Gomtiotrematinae Gupta, 1955 Allogomtiotrematinae Yamaguti, 1958 Proterometrinae Yamaguti, 1958 large; occasionally small. Ventral sucker larger or smaller than oral sucker; in middle or anterior half of body. Testes in tandem, oblique or symmetrical; post-ovarian. Uterus entirely pre-testicular. Vitelline field may extend into forebody. Excretory arms may or may not unite in forebody. Parasitic in stomach or body-cavity of elasmobranchs and stomach of fresh- Body normally water teleosts and holosteans. Key 1 . to Azygiinae A. Testes symmetrical ; vitelline follicles and uterine coils extending into forebody ; testes near posterior extremity; in freshwater teleosts (N. America) Testes tandem, oblique, or occasionally symmetrical; vitelline follicles and uterine coils entirely or almost entirely confined to hindbody; testes usually well anterior to posterior . B. extremity 2. ......... . . PROTEROMETRA . ...... ..... A. Vitelline follicles confluent posterior to testes; ventral sucker sucker; parasitic in elasmobranchs. B. Vitelline follicles not confluent posterior to testes; oral sucker sucker; parasitic in freshwater teleosts and holosteans normally larger than oral OTODISTOMUM normally larger than ventral AZYGIA THE HEMIUROIDEA AZYGIA 61 Looss, 1899 [t(w,s)] Megadistomum Stafford, 1904 Mimodistomum Stafford, 1904 Hassallius Goldberger, 1911 Eurostomum MacCallum, 1921 Gomtiotrema Gupta, 1955, nee Sinha, 1934 Allogomtiotrema Yamaguti, 1958 Body medium to large; usually elongate, occasionally oval. Ventral sucker smaller than oral sucker; in anterior half of body. Testes tandem, occasionally to symmetrical; anterior testis occasionally lateral to ovary (A. asiatica). Sinus-organ a small papilla-like structure. Uterine between ovary and ventral sucker. Vitelline follicles confined to hindbody; not confluent posterior to testes. Excretory arms apparently not united in forebody. Parasitic in stomach and intestine of freshwater teleosts and holosteans. field TYPE-SPECIES. Azygia lucii (Mu'ller, 1776) [by subsequent designation: Goldberger, 191 la]. two subgenera, Azygia Looss, 1899, and Pseudazygia the length of the post-testicular region and the position of the bifurcation of the excretory vesicle. The former criterion appears to be a somewhat variable feature in Azygia asiatica Simha & Pershad, 1964, and in A. angusticauda (Stafford) of Kakaji COMMENT. Yamaguti Yamaguti, 1971. (1968; ? (1971) recognizes He distinguishes these by synonym of A. asiatica). OTODISTOMUM Stafford, 1 904 [t(w,s) ; n(w,s)] Xenodistomum Stafford, 1904 Josstaffordia Odhner, 1911* Aphanhystera Guiart, 1938 large; spatulate to elongate. Ventral sucker larger than oral sucker; close to anterior extremity. Testes tandem or slightly oblique. Sinus-organ capable of considerable extension or contraction to form small papilla. Uterine field almost entirely between ovary and ventral sucker. Body Vitelline follicles extend in lateral fields posterior to ventral sucker, reaching back to posttesticular region where fields are confluent. Excretory arms usually unite in forebody, but occas- ionally do not. Parasitic in stomach or body-cavity of elasmobranchs (sharks, rays and chimaeras). TYPE-SPECIES. Otodistomum veliporum (Creplin, 1837) [by monotypy]. COMMENT. It is worth noting that there are two body-forms present to be related to their location within the host. in this genus, which appear The species parasitic within the body-cavity tend to be broad or spatulate, whilst those parasitic in the stomach are very elongate. It is possible that the spatulate body-shape has been evolved to prevent these parasites being lost through the abdominal pores, and it is noticeable that the gorgoderid and monogenean parasites from the body-cavity of elasmobranchs are also spatulate or oval. Elasmobranchs are the only group of vertebrates which commonly harbour adult helminths in the body-cavity: this is because the abdominal pores form an exit for the release of eggs. The excretory arms in species of Otodistomum are normally considered to unite in the forebody; but in sectioned material of O. plunketi Fyfe, 1953, they end blindly (Gibson & Bray, 1977). PROTEROMETRA Horsfall, 1933 oval; small. Oral sucker large; ventral sucker small, situated at or just posterior to middle of body. Testes symmetrical at posterior extremity. Sinus-organ a small cone. Uterine field extends from ovary into forebody. Vitellarium extends from level of testes or ovary anteriorly Body * The appellation Josstaffordia josstaffordi n.g., n.sp. was proposed by Odhner (1911) for specimens of Otodistomum in a sarcastic footnote, mimicking the erection of Hassallius hassalli by Goldberger (191 la). Although he gives indications as to its distinctive features, it is obvious that Odhner did not intend it to be considered valid. 62 D. I. GIBSON & R. A. BRAY well into forebody, in lateral fields. Excretory arms united water teleosts (in North America). in forebody. Parasitic in gut of fresh- TYPE-SPECIES. Proterometra macrostoma (Faust, 1918) [by monotypy]. Subfamily LEUCERUTHRINAE Goldberger, 1911 Body medium to large; elongate oval. Ventral sucker smaller than oral sucker; near middle of body. Testes oblique; pre-ovarian; immediately posterior to ventral sucker. Prostatic sac small. Sinus-organ small, but well defined. Uterine field between ovary and ventral sucker, passing between testes. Vitelline follicles in lateral fields, extending almost throughout length of hindbody. Excretory arms unite in forebody. Parasitic in gut of freshwater teleosts and holosteans (in North America). LEUCERVTHRUS Marshall & Gilbert, 1905 Defined as subfamily. TYPE-SPECIES. Leuceruthrus micropteri Marshall & Gilbert, 1905 [by monotypy]. BATHYCOTYLIDAE Family Dollfus, 1932 Body large; elongate, but stout. Ecsoma absent. Body-surface smooth, but may be wrinkled. Oral and ventral suckers well developed; latter just in anterior half of body. Pharynx well developed. Oesophagus short. 'Driisenmagen' present. Gut-caeca end blindly close to posterior extremity. Testes two; tandem; separated by ovary; in mid-hindbody. Seminal vesicle thin-walled; tubular; convoluted; small; well forward in forebody. Pars prostatica tubular; indistinct. Sinusorgan and sinus-sac absent. Genital atrium small, but deep. Genital pore mid-ventral close to posterior margin of oral sucker. Ovary oval to reniform; inter-testicular. Mehlis' gland posterior or lateral to ovary. Laurer's canal [see below] and uterine seminal receptacle present. Juel's organ and canalicular or blind seminal receptacle absent. Uterus fills much of hind- and forebody. Eggs numerous; small; non-filamented. Vitellarium several filamentous tubules in hindbody. Excretory vesicle Y-shaped; arms united in forebody. Parasitic on gills (? or in stomach) of pelagic marine teleosts (scombrids and Coryphaend). BATHYCOTYLE Darr, 1902 [n(w,s)] Defined as family. TYPE-SPECIES. Bathycotyle branchialis Darr, 1902 [by monotypy]. COMMENT. Although Yamaguti (19380) states: 'Laurer's canal apparently without external opening', when describing Bathycotyle coryphaenae Yamaguti, 1938, it is obvious that a dorsal pore does occur in the type-species, as Dollfus (1932) clearly illustrated it in his figure failed to section his material. guti, however, in contrast to Dollfus, apparently Family BUNOCOTYLIDAE 5. Yama- Dollfus, 1950 Body usually small; fusiform to elongate. Distinct ecsoma absent, but vestige may remain. Bodysurface smooth or with plications. Ridges around body often present at level of oral sucker and posterior margin of ventral sucker. Ventral sucker normally inside anterior half of worm. Pharynx well developed. Oesophagus normally short. 'Driisenmagen' normally present. Gut-caeca normally end blindly near posterior extremity or occasionally form cyclocoel. Testes two; preovarian in hindbody; tandem to symmetrical. Seminal vesicle saccular or tubular; in fore- or hindbody. Pars prostatica tubular or vesicular; short or long; may extend into hindbody. Ejaculatory duct long, short or apparently absent. Sinus-sac usually present, occasionally absent. Hermaphroditic duct present; within sinus-sac when latter present. Permanent sinus-organ THE HEMIUROIDEA 63 normally absent, but temporary sinus-organ may form. Genital atrium small or absent. Ovary between testes and vitellarium. Mehlis' gland post-ovarian. Laurer's canal bilobed; oval; rarely and canalicular seminal receptacle absent. Juel's organ and uterine seminal receptacle present or absent. Blind seminal receptacle present or absent. Uterus normally almost entirely in hindbody; mainly pre- to mainly post-ovarian. Eggs numerous; small; without filaments. Vitellarium one or two, occasionally three, entire (rarely slightly lobed) masses; posterior or postero-lateral to ovary. Excretory arms rarely fail to unite in forebody; stem of excretory vesicle often with terminal bulb or with large pore (actual pore may be withdrawn within vestige of ecsoma). Parasitic mainly in stomach of marine teleosts. Key 1. 2. to Bunocotylidae A. Uterine seminal receptacle present; vitellarium 1 or 2 masses Blind seminal receptacle present; body-surface smooth; vitellarium 2 or A. Parasites B. Parasites small, rarely more than 2 in length, commonly less than tration of uterine coils not present between ovary and testes A. Body-surface smooth; ridges present around body at level of oral sucker and posterior margin of ventral sucker; major part of uterine field pre-ovarian; vitellarium single B. Body-surface usually plicated, occasionally smooth; ridges around body at level of sucker absent; large or major part of uterine field post-ovarian; vitellarium single or double testes 3. ..... B. up to 6mm (p. 66) concentration of uterine coils between ovary and . mm THELETRINAE (p. mm; large concen- ..... 1 BUNOCOTYLINAE APHANURINAE Subfamily 2 masses OPISTHADENINAE in length; large . . 3 BUNOCOTYLINAE 69) 3 (p. 63) (p. 64) Dollfus, 1950 ecsoma may be present. Body-surface smooth. Ridges present around and posterior margin of ventral sucker; additional ridge often present close to posterior extremity. Transverse septate partitions of body may occur. Gut-caeca end blindly or form cyclocoel. Testes tandem to oblique; not separated from ovary by large concen- Body body small. Vestige of at level of oral sucker tration of uterine coils. Seminal vesicle saccular; oval to elongate; in forebody or dorsal to ventral sucker. Pars prostatica short; tubular or vesicular. Sinus-sac absent or small and tubular to oval. Short hermaphroditic duct may extend to form temporary sinus-organ. Genital atrium absent or Ovary oval. Uterine seminal receptacle present (?). Juel's organ not reported. Blind seminal receptacle absent. Vitellarium a single, unlobed mass; immediately post-ovarian. Excretory small. vesicle expanded distally; arms united in forebody; pore wide. Parasitic in gut of freshwater and euryhaline teleosts; occasionally progenetic in snails and copepods. COMMENT. According to the literature, the type of seminal storage apparatus occurring in this subfamily is a matter of some disagreement. Manter (1969a) observed a uterine seminal receptacle in Saturnius segmentatus Manter, 1969, whereas Yamaguti (1970) described a seminal receptacle in S. mugilis (Yamaguti, 1970). Overstreet (1977), when re-defining Saturnius, stated that a seminal receptacle was absent. No seminal storage apparatus has been described for Bunocotyle cingulata Odhner, 1928, by Odhner (19286) or for B. progenetica (Markowski, 1936) by Deblock (1975). We have examined sections of a paratype specimen of Saturnius papernai Overstreet 1977, and confirm that: (1) a distinct seminal receptacle (canalicular or blind) and Laurer's canal are absent; and (2) spermatozoa are present in the proximal region of the uterus, which thus functions as a uterine seminal receptacle. We could not for certain distinguish Juel's organ, but it is possible that in the small species which constitute this subfamily, this structure is reduced or lost altogether. It is conceivable that the transverse ridge around the posterior extremity in some species of this subfamily, and possibly both the ampullaceous nature of the distal region of the stem of the excretory vesicle and the wide excretory pore, represent vestiges of an ecsoma. Overstreet (1977) has described the former as a possible small ecsoma in S. maurepasi Overstreet, 1977, where, in the living worm, it may be partly withdrawn. 64 D. Key 1. I. GIBSON & R. A. BRAY to Bunocotylinae A. B. Transverse fibrous septa in fore- and hindbody; cyclocoel absent; sinus-sac present; SATURNIUS parasitic in euryhaline teleosts (Mugil) Transverse septa not present; cyclocoel present; sinus-sac absent; parasitic in freshwater or euryhaline teleosts, or progenetic in snails and copepods BUNOCOTYLE . BUNOCOTYLE Odhner, . 1928 Transverse fibrous septa absent. Cyclocoel present. Sinus-sac absent. Uterine seminal receptacle (?) presumed to be present. Parasitic in gut of freshwater or euryhaline teleosts, or progenetic in snails and copepods. TYPE-SPECIES. Bunocotyle cingulata Odhner, 1928 [by original designation]. COMMENT. See Theletrum for comment on B. sudatlantica Parukhin, 1976. SATURNIUS Manter, 1969 [n(w,s)] Small papillae or corrugations may be associated with suckers. Internal transverse, fibrous septa present in fore- and hindbody. Gut-caeca end blindly. Sinus-sac may contain ejaculatory (? hermaphroditic) vesicle. Parasitic in, and under lining of, stomach of euryhaline teleosts (Mugil cephalus). TYPE-SPECIES. Saturnius segmentatus Manter, 1969 [by original designation]. COMMENT. This genus has recently been revised by Overstreet (1977), who has cleared up many of the discrepancies between the descriptions of S. segmentatus and S. mugilis (Yamaguti, 1970). Subfamily APHANURINAE Skrjabin & Guschanskaja, 1954 [28.4.1954] Ahemiurinae Chauhan, 1954 [17.11.1954] small. Vestige of ecsoma may be present. Body-surface usually with distinct annular plications, occasionally ( ?) smooth [some species of Aphanums]. Ridges around body at level of suckers absent. Gut-caeca end blindly near posterior extremity. Testes tandem to symmetrical; normally well posterior to ventral sucker; not separated from ovary by large concentration of uterine coils. Seminal vesicle tubular in forebody, or saccular (oval, elongate or bipartite) in hindbody (or at least posterior to middle of ventral sucker). Pars prostatica tubular or vesicular; short or long. Ejaculatory duct long, short or apparently absent. Sinus-sac present, enclosing hermaphroditic duct, or (?) absent. Ovary oval; immediately or almost immediately posttesticular. Blind seminal receptacle absent. Uterine seminal receptacle and ( ?) JueFs organ present. Large or major part of uterine field post-ovarian. Vitellarium one or two compact Body normally masses; usually immediately posterior, occasionally lateral, to ovary. Excretory arms united in forebody; excretory pore often large; actual pore may be withdrawn within vestige of ecsoma. Parasitic mainly in stomach or oesophagus of marine teleosts. COMMENT. A small 'seminal receptacle' has been reported for Duosphincter by Yamaguti (1970) and in some species of Aphanurus. A uterine seminal receptacle has been reported for Myosaccium and other species of Aphanurus. It is likely that the reports of a 'seminal receptacle' from this group are mistaken, as Juel's organ and a uterine seminal receptacle are easily mistaken for such a structure in whole-mount preparations. The genera of this group are essentially typical hemiurids which have lost their ecsoma. The presence of records from the oesophagus suggests that these parasites may inhabit the less acidic anterior regions of the stomach, and do not have the same requirement for an ecsoma as the closely related forms which tend to inhabit the pyloric region of the stomach. THE HEMIUROIDEA Key 1. 2. to Vitellarium B. Vitellarium A. Seminal vesicle tubular, winding in forebody DUOSPHINCTER Seminal vesicle saccular (oval, elongate or bipartite; often attenuated anteriorly), posterior to middle of ventral sucker 3 Pars prostatica vesicular, with muscular wall MYOSACCIUM Pars prostatica tubular 4 Seminal vesicle oval sinus-sac present AHEMIURUS Seminal vesicle apparently bipartite and attenuated anteriorly; sinus-sac apparently absent A. B. 4. ..... ....... ..... .......... ........... ....... composed of 2 composed of 1 A. B. 3. Aphanurinae 65 A. B. ; distinct masses distinct mass 2 APHANURUS APHANUROIDES APHANURUS Looss, 1907 [n(w)] Chauhanurus Skrjabin & Guschanskaja, 1954 Helaphanurus Slusarski, 1957 Body-surface normally plicated, occasionally ( ?) smooth. Testes oblique, occasionally symmetrical or tandem. Seminal vesicle oval to elongate oval; in hindbody; wall may be muscular. Pars prostatica tubular; long. Ejaculatory duct long or short. Sinus-sac present; tubular. Temporary sinus-organ sometimes present as small cone. Vitellarium a single, large, entire or slightly indented, post-ovarian mass. Parasitic in oesophagus and stomach of essentially marine teleosts from marine and brackish water environments. TYPE-SPECIES. Aphanurus stossichi (Monticelli, 1891) [by original designation]. COMMENT. There has been considerable comment in the literature (Looss, 1908; Rioja, 1923; Chauhan, 1954; Slusarski, 1957) as to whether Aphanurus possesses or lacks a small vestigial ecsoma. Although this question has not been resolved, Chauhan (1954) suggested that the confusion may have been caused by the bulbous nature of the excretory vesicle. The possible vestiges of an ecsoma, however, may be a common feature of both the aphanurines and the bunocotylines. Some species of Aphanurus (A. caesionis Yamaguti, 1952 and A. dorosomatis Yamaguti, 1953) are reported to have a smooth body-surface; but, as they are known from only one or two specimens, this requires confirmation. If this is proved to be correct, then there may be grounds for distinguishing them from the other species of Aphanurus at the generic level. AHEMIURUS Chauhan, 1954 Testes symmetrical to oblique. Seminal vesicle oval; in hindbody. Pars prostatica tubular; long. Ejaculatory duct long. Sinus-sac present; elongate oval. Vitellarium two oval, compact masses; symmetrical; post-ovarian. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Ahemiurus karachii (Srivastava, 1937) [by original designation]. COMMENT. Yamaguti (1971) lists Ahemiurus as a synonym of Opisthadena despite the fact that Chauhan (1954) emphasized the presence of cuticular plications in this species. The latter is a feature which occurs only in hemiurid and aphanurine genera. Although the seminal storage apparatus of the genus has not been described, we expect it to conform to the subfamily definition. (?) APHANUROIDES Nagaty & [Inadequately described.] Testes tandem. Abdel-Aal, 1962 Seminal vesicle saccular; ( ?)bipartite attenuated and posterior half of ventral sucker. Pars prostatica tubular. [Terminal genitalia not described in detail.] Sinus-sac (?) absent. Short hermaphroditic duct and genital atrium apparently present. [Figures of Nagaty & Abdel-Aal, 1962, suggest that anteriorly; extending between anterior ; testis temporary sinus-organ may form (?).] Vitellarium two compact masses; symmetrical to oblique; post-ovarian. Excretory arms (?). Parasitic in gut of marine teleosts. 66 D. I. GIBSON & TYPE-SPECIES: Aphanuroides lethrini Nagaty & DUOSPHINCTER BRAY R. A. Abdel-Aal, 1962 [by original designation]. Manter & Pritchard, 1960 Strongly developed sphincter muscles surround apertures of suckers. Testes oblique to tandem. Seminal vesicle tubular; winding in forebody. Pars prostatica tubular; short. Sinus-sac small; oval. Temporary sinus-organ may form. [Small seminal receptacle (? Juel's organ) present, according to Yamaguti, 1970.] Vitellarium two oval masses; oblique to tandem; immediately post-ovarian. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Duosphincter zancli Manter & Pritchard, 1960 [by monotypy]. MYOSACCIUM Montgomery, Neogenolinea Siddiqi & 1957 Cable, 1960. Testes symmetrical to tandem. Seminal vesicle saccular; attenuated anteriorly; at level of posterior margin of ventral sucker. Pars prostatica vesicular; with strong, muscular wall; in forebody. [Terminal genitalia confused in literature.] Sinus-sac apparently tubular; enclosing hermaphroditic duct, which may form temporary sinus-organ. Eggs without filament [the structure of collapsed eggs may apparently give the impression that a short filament and spine are present (?)]. Vitellarium two oval or slightly indented masses; oblique to tandem; one mass usually lateral, other immediately postero-lateral or posterior, to ovary. Parasitic in stomach of marine teleosts (Clupeidae). TYPE-SPECIES. Myosaccium ecaude Montgomery, 1957 [by original designation]. COMMENT. There appears to be some difference of opinion with regard to the presence or absence of filaments on the eggs. Montgomery (1957) and Kohn & Buhrnheim (1964) indicate that a filament is present with, in the case of the latter authors, an additional small spine at the opposite end of the egg. Overstreet (1969) and Yamaguti (1971), after examining some of Montgomery's type-specimens, state that filaments on the egg could not be seen. Overstreet suggests that the so-called filaments described in this genus may be an artifact present in collapsed eggs. Subfamily Intuscirrinae Skrjabin & OPISTHADENINAE Yamaguti, 1970 Guschanskaja, 1959 Body spindle-shaped to elongate. Body-surface smooth. Transverse ridges in body-wall present or absent around body at level of oral sucker and/or posterior margin of ventral sucker [these are often not obvious]. Presomatic pit reported (?) in Mitrostoma. Gut-caeca end blindly near tandem to oblique; usually well posterior to ventral sucker and near from not ovary by large concentration of uterine coils. Seminal vesicle tubular separated ovary; to saccular (? rarely bipartite); in fore- or hindbody. Pars prostatica long or short; tubular or vesicular. Ejaculatory duct long to short or apparently absent. Sinus-sac present; oval to elongate posterior extremity. Testes oval; enclosing hermaphroditic duct. Sinus-organ (? temporary) occasionally present. Genital atrium usually present; small. Ovary normally oval, occasionally bilobed; normally close to testes. Blind seminal receptacle present; large; usually dorsal or antero-dorsal to ovary. Juel's organ and uterine seminal receptacle absent. Uterus mainly pre- to mainly post-ovarian. Vitellarium two, occasionally three, entire or slightly indented masses; posterior or postero-lateral to ovary. Excretory arms usually, but not always, united in forebody. Parasitic in stomach, occasionally intestine, of marine teleosts. COMMENT. The presence of ridges (tegumental folds) around the body, especially the one immediately posterior to the ventral sucker, may well be a good generic criterion. We are concerned about the significance of this feature, as it is often very difficult to see, and in genera such as Genolinea, where it is known to occur, it has only been reported occasionally. THE HEMIUROIDEA Key 1. to Opisthadeninae A. B. 2. A. B. 3. A. B. 67 ......... Seminal vesicle entirely in hindbody Seminal vesicle in forebody (occasionally dorsal or postero-dorsal to ventral sucker) Ejaculatory duct short or absent; pars prostatica reaches forward to level of caecal bifurca. ...... ..... . 2 3 MITROSTOMA tion; (?) presomatic pit apparently present Ejaculatory duct long; pars prostatica does not reach further forward than ventral sucker; OPISTHADENA presomatic pit absent Vitellarium 2 symmetrical, oblique or tandem masses GENOLINEA Vitellarium 3 masses, the anterior pair being symmetrical and the posterior mass being the NEOTHELETRUM largest OPISTHADENA Linton, 1910 Body elongate. Transverse ridge (fold) of body-wall around body immediately posterior to ventral sucker. Testes tandem; posterior to middle of body. Seminal vesicle in hindbody; usually tubular and sinuous, but reported as enclosed within muscular, ovoid sac ['seminal sac' of Manter, 1947] or as being saccular. Pars prostatica tubular; not reaching further forward than posterior margin of ventral sucker. Ejaculatory duct long. Sinus-sac oval. Hermaphroditic duct may be sub-divided. Sinus-organ apparently present as small cone, at least temporarily. Ovary close to testes. Uterus mainly pre-ovarian. Vitellarium two symmetrical to oblique masses; postovarian. Excretory arms diverticulate; united in forebody. Parasitic in stomach of marine teleosts (especially Kyphosus}. TYPE-SPECIES. Opisthadena dimidia Linton, 1910 [by original designation]. GENOLINEA Manter, 1925 [t(w,s); n(w,s)] Parasterrhurus Manter, 1934 Intuscirrus Acena, 1947 Pseudobunocotyla Yamaguti, 1965 Body spindle-shaped to slightly elongate. Transverse ridge usually present around body immedia- sucker (often inconspicuous and frequently not reported); similar ridge may surround oral sucker. Large pre-oral lobe may be present. Ventral sucker normally in anterior half of body, (?) occasionally near middle; sphincter muscles sometimes present around aperture. Testes tandem to oblique; close to ovary. Seminal vesicle small; tubular; convoluted in forebody, occasionally dorsal or postero-dorsal to ventral sucker. Pars prostatica tubular to vesicular; short. Ejaculatory duct short or absent. Sinus-sac oval to elongate oval; small. Sinusorgan occasionally present (? temporary). Ovary near middle of hindbody. Uterus usually in both tely posterior to ventral pre- and post-ovarian fields, occasionally post-vitelline distribution is limited. Metraterm reported in some instances to be spinous (?). Vitellarium two compact (occasionally lobed), symmetrical, oblique or tandem masses; posterior or postero-lateral to ovary. Excretory arms united in forebody. Parasitic mainly in stomach of marine teleosts. TYPE-SPECIES. Genolinea lalicauda Manter, 1925 [by original designation]. COMMENT. The position of the ventral sucker near the middle of the body in G. dactylopagri further Manter, 1954, posterior than normally occurs in this family. The morphology of this species suggests that it is related to Lewodera Linton, 1910, as Manter (1954) initially believed, and both are recorded from related percoid families of teleosts. is much MITROSTOMA Manter, 1954 Body elongate. Thickened projection present on each side of body at level of posterior margin of ventral sucker. Nipple-shaped protuberance (? vestige of ecsoma) may be present at posterior extremity. Weakly muscled pre-oral lobe bears mouth. Structure resembling (?) presomatic pit apparently present anterior to ventral sucker. Ventral sucker with 'sphincter muscles in anterior and posterior halves'. Testes tandem; close to ovary; near middle of hindbody. Seminal vesicle 68 D. I. GIBSON & R. A. BRAY tubular; convoluted; entirely in hindbody. Pars prostatica tubular; reaches forward to caecal bifurcation. Ejaculatory duct short or absent. Sinus-sac short; pyriform; (?) protrusible. Ovary in posterior half of hindbody. Uterus mainly pre-ovarian, but does extend into post-vitelline region. Vitellarium two oblique to symmetrical, post-ovarian masses. Excretory arms united in forebody. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Mitrostoma nototheniae Manter, 1954 [by original designation]. COMMENT. There are several features of the genus Mitrostoma, such as the overall arrangement of the organs, the apparent presence of a presomatic pit and the reported presence of a nipple-shaped protuberance at the posterior extremity of one specimen, which suggests that it might be a hemiurid with a lost or vestigial ecsoma, no longer required because of its intestinal habitat. Manter (1954), however, reported that a blind seminal receptacle was present. The presence of this type of seminal receptacle, as opposed to a uterine seminal receptacle, and the great morphological similarity between this parasite and Genolinea bowersi (Leiper & Atkinson, 1914), reported from related nototheniid hosts (Prudhoe is probably correct. & Bray, 1973), indicate that position within the Opistha- its deninae NEOTHELETRUM gen. nov. small; elongate to spindle-shaped. Tegumental fold around body posterior to ventral sucker apparently absent. Body-surface smooth. Ventral sucker in anterior half of body. Pre-pharynx absent. Pharynx well developed. Oesophagus short; often with small diverticulum. Gut-caeca end Body blindly near posterior extremity. Testes 2; oval; oblique to symmetrical; usually separated from ventral sucker by loops of uterus; occasionally sandwiched between ventral sucker and ovary. Seminal vesicle small tubular to saccular ( ? occasionally bipartite) in forebody. Pars prostatica ; ; short; tubular to vesicular. Ejaculatory duct short or absent. Sinus-sac small; oval. Small temporary sinus-organ may form. Hermaphroditic duct short; formed within sinus-sac. Genital atrium small. Genital pore mid-ventral in forebody. Ovary oval (may occasionally be bilobed); near middle of hindbody. Blind seminal receptacle antero-dorsal to ovary. Laurer's canal, Juel's organ and both canalicular and uterine seminal receptacle presumably absent. Uterus almost entirely in hindbody; usually with roughly equal amounts in pre- and postovarian fields; occasionally with majority of uterus in post-ovarian field. Eggs small; numerous; without filaments. Vitellarium three compact, entire or slightly indented masses; anterior pair symmetrical, connected by narrow isthmus; posterior mass larger, may be slightly bilobed [vitellarium is essentially two tandem masses, the anterior of which is divided into two distinct lobes: the vitellarium may appear as two tandem masses in lateral view]; post-ovarian. Excretory arms united in forebody or not. Parasitic in stomach of marine teleosts. post-testicular; TYPE-SPECIES. Neotheletrum lissosomum (Manter, 1940) n. comb. COMMENT. Neotheletrum differs from Theletrum much of the is present; (2) testes; (3) the anterior vitelline receptacle in that: (1) a blind rather than a uterine seminal post-ovarian rather than being between the ovary consistently divided into two; and (4) the tegumental uterus is mass is the around immediately posterior to the ventral sucker is absent. body ridge The additional species which we include in this genus are as follows N. frontilatum (Manter, 1969) n. comb. N. gravidum (Manter, 1940) n. comb. N. magnasaccum (Sogandares-Bernal & Sogandares, 1961) n. comb, [possibly a synonym of N. lissosomum]. N. pomacentri (Nahhas & Cable, 1964) n. comb. N. frontilatum, which Yamaguti (1971) considers to belong to Hysterolecithoides, differs from the and : other species of Neotheletrum in that the uterus is almost entirely post-ovarian, the testes are close behind the ventral sucker and close to the ovary, and the excretory arms are not united in the forebody. On these grounds a case could be made for erecting a new genus for this species; but we have present. included it in Neotheletrum as there seems little point in further sub-division at THE HEMIUROIDEA THELETRINAE 69 subfam. nov. Body elongate. Ecsoma absent. Body-surface smooth papillae may be present ventrally in foreor hindbody; transverse ridge may be present around body near posterior margin of ventral sucker and possibly around oral sucker. Oral and ventral suckers well developed ventral sucker in anterior half of body. Prepharynx absent. Pharynx well developed. Oesophagus short. Gutcaeca end blindly near posterior extremity, (?) or at level of ovary. Testes two; pre-ovarian; tandem to oblique; near middle of hindbody; separated from ovary by majority or large part of uterine coils. Seminal vesicle tubular or (?) saccular; in forebody, but sometimes reaching back to ; ; posterior margin of ventral sucker. Pars prostatica short; tubular or slightly vesicular. Ejaculatory duct short or apparently absent. Sinus-sac usually small; oval or elongate oval; weakly developed; enclosing hermaphroditic duct; may extrude slightly through genital pore. Permanent sinusorgan absent (?), but temporary sinus-organ may form. Genital atrium small or absent. Ovary oval ; near posterior extremity or at least well inside posterior half of hindbody. Laurer's canal and both canalicular or blind seminal receptacle absent [Laurer's canal reported present (?) in Indoderogenes], Uterine seminal receptacle present. Juel's organ assumed to be present. Uterus almost entirely or mainly in hindbody (small part of uterus is coiled in forebody of Monolecithotremd) mainly pre-ovarian, with large proportion of uterine coils between ovary and testes. Eggs numerous; small; without filaments. Vitellarium one entire or two tandem to oblique, entire or slightly lobed masses posterior or postero-lateral to ovary. Excretory vesicle Y-shaped arms united in forebody. Parasitic normally in stomach of marine teleosts. ; ; ; COMMENT. This subfamily is erected for forms which resemble the Opisthadeninae; but lack a blind seminal receptacle, possess a uterine seminal receptacle (plus presumably Juel's organ) and contain a large concentration of uterine coils between the ovary and testes. The position of Indoderogenes Srivastava, 1937, discussed below, is problematical; but in gross morphology it does appear to key satisfactorily to this subfamily. The sinus-sac in both Theletrum and Monolecithotrema often appears to be slightly extruded through the genital pore. It is not clear from our observations of the type-species if this is in fact so, or whether a temporary sinus-organ is formed by an eversion of the hermaphroditic duct. Key 1 . to Theletrinae A. Vitellarium single (great care should be taken with this observation, as at certain angles the vitellarium of Theletrum appears to be single); transverse ridge posterior to ventral sucker absent; some uterine coils in forebody B. Vitellarium double; uterus not coiled in forebody Seminal vesicle tubular; transverse ridge normally present posterior to ventral sucker; gut-caeca terminate near posterior extremity ....... ...... . 2. A. . . . MONOLECITHOTREMA 2 THELETRUM B. Seminal vesicle saccular; transverse ridge posterior to ventral sucker not reported; gutcaeca apparently terminate at level of anterior margin of ovary. INDODEROGENES . THELETR UM Linton, 1910 [t( w)] Transverse tegumental ridge present around body immediately posterior to ventral sucker and possibly around oral sucker. Papillae may be present ventrally in hindbody. Gut-caeca terminate at posterior extremity. Testes fairly close together, but separated by uterus. Seminal vesicle tubular. Pars prostatica slightly vesicular. Sinus-sac elongate oval; thin-walled; sheath-like; may be partly extruded through genital pore. Ovary close to posterior extremity. Uterine coils enor almost entirely in hindbody; few or no coils posterior to vitellarium. Vitellarium two oblique, entire or slightly lobed masses; close together; posterior or postero-lateral to ovary; at posterior extremity of body. Parasitic in stomach (occasionally intestine) of marine teleosts. tirely TYPE-SPECIES. Theletrum fust iforme Linton, 1910 [by original designation]. We agree with Yamaguti (1971) that this genus is monospecific. We do not agree, however, that the remainder of the species allocated to this genus should be placed in Genolinea Manter, 1925, and have, therefore, erected a new genus, Neotheletrum, in the Opisthadeninae to COMMENT. 70 D. accommodate them (see p. 68). Our I. GIBSON & R. A. BRAY observations of the type-species confirm that a uterine seminal receptacle is present as indicated by Yamaguti's (1971) and possibly Vigueras' (1958) figures. Bunocotyle sudatlantica Parukhin, 1976, may belong to this genus, as it possesses many morphological similarities and is recorded from the same family of host (Chaetodontidae). Parukhin's (19760) description, however, indicates that there is a single vitelline mass and a cyclocoel present. Nevertheless, when viewed from certain angles T. just ifor me can appear to possess only one vitelline mass, and the presence or absence of a cyclocoel is often difficult to ascertain in this family. Certainly, Parukhin's material does not fit within our concept of Bunocotyle. (^INDODEROGENES Srivastava, 1937 Transverse ridge around body posterior to ventral sucker apparently absent. Gut-caeca terminate close to anterior margin of ovary. Testes separated by uterine coils. Seminal vesicle saccular (flask-shaped). Pars prostatica tubular. Sinus-sac (?) absent. Hermaphroditic duct short. Sinus- organ small ( ? temporary). Genital atrium small. Ovary close to posterior extremity. Laurer's canal reported present (?). Uterine coils entirely or almost entirely in hindbody; entirely or almost entirely pre-ovarian. Vitellarium two tandem to oblique masses; posterior or posterolateral to ovary at posterior extremity of body. Parasitic in stomach of marine teleosts. ; TYPE-SPECIES. Indoderogenes purii Srivastava, 1937 [by monotypy]. COMMENT. This genus, initially defined in an abstract by Srivastava (19376) and later (1941) described in more detail, is known from only three specimens. In gross morphology it appears similar to the other two genera of this subfamily, although Srivastava (1941) reported the presence of Laurer's canal. We have some doubts about this, as such an observation on whole-mounts with field, as his figure indicates, must be questionable. Despite the fact that no mention was made by Srivastava of the presence of a sinus-sac, there may have been one present, as this structure is either small or weakly developed in the other genera of this subfamily. If Laurer's canal is proved to be present by future workers, this genus should be transferred to the Halipeginae Poche, 1926, where, although sharing some of its features with Deropegus McCauley & Pratt, 1961, its gross morphology does not conform to the normal derogenid pattern. In addition, unlike the majority of halipegines this genus was recorded from a marine teleost, although the locality of the record, an almost land-locked bay in the Bay of Bengal, is brackish a large, dense uterine at certain times of the year. MONOLECITHOTREMA Yamaguti, 1970 [T(w)] Transverse ridges around body absent. Papillae may be present ventrally in forebody. Gut-caeca terminate blindly at posterior extremity. Testes close together, but sometimes separated by uterus. Seminal vesicle tubular usually extending back dorsally to ventral sucker. Pars prostatica tubular; poorly developed linked to seminal vesicle by aglandular duct. Sinus-sac small poorly developed may be slightly extruded through genital pore. Ovary well inside posterior half of hindbody. Small proportion of uterus may be coiled in forebody; small part of uterus extends posteriorly to ; ; ; vitellarium. Vitellarium of marine one large, entire ; mass; immediately post-ovarian. Parasitic in stomach teleosts. TYPE-SPECIES. Monolecithotrema kala Yamaguti, 1970 [by original designation]. 14 paratype-specimens mounted on a single slide shows that a uterine seminal receptacle is present, and that Yamaguti was probably mistaken in his observation of a small seminal receptacle between the ovary and the vitellarium. This structure corresponds with the position of Mehlis' gland, but might also have been part of the uterine seminal receptacle, JuePs organ (until sectioned material is examined we are assuming that this is present) or even a diverticulum of the gut-caeca. As in Theletrum, the uterine seminal receptacle tends to extend COMMENT. Examination of posteriorly to the vitellarium. THE HEMIUROIDEA Family DEROGENIDAE 71 Nicoll, 1910 Halipegidae Poche, 1926 Liocercidae Ejsmont, 1931 Body normally small; usually spindle-shaped to elongate oval. Ecsoma absent. Body-surface smooth. Oral and ventral suckers well developed; ventral sucker usually near middle of body, more anterior or posterior. Pharynx well developed. Oesophagus short. 'Driisenmagen' usually present. Gut-caeca end blindly or form cyclocoel. Testes two; symmetrical to tandem; pre- or post-ovarian; in hindbody. Seminal vesicle thin- walled; oval, elongate or tubular; occasionally not constricted into portions; in forebody; occasionally partly or wholly enclosed within sinussac. Pars prostatica usually tubular, occasionally vesicular; occasionally enclosed within sinussac. Ejaculatory duct short or absent; often within sinus-sac. Sinus-sac normally present, occasionally absent usually small and oval often weakly developed may enclose all or part of pars prostatica and seminal vesicle. Permanent sinus-organ present as small cone or absent. Hermaphroditic duct normally present; occasionally absent; usually short. Genital atrium present or absent; usually small. Genital pore mid-ventral in forebody. Ovary oval; pre- or post-testicular. Mehlis' gland normally post-ovarian or occasionally at level of ovary. Seminal storage and disposal apparatus variable. Laurer's canal usually present; either opening dorsally to exterior or leading into Juel's organ often dilated proximally to form small rudimentary seminal receptacle, ; ; ; ; occasionally enlarged to form an apparently functional canalicular seminal receptacle. Juel's organ absent or present in either rudimentary or fully-developed state. Blind seminal which is receptacle present rarely. Uterine seminal receptacle normally present; rarely absent. Uterus may or may not extend posterior to vitellarium significant proportion of uterus usually coiled in ; forebody. Eggs numerous; with or without filaments or threads; rarely with anopercular spine. Vitellarium one or two masses entire or lobed (lobes normally shallow, rarely digitate) pre- or post-ovarian; symmetrical, oblique or tandem. Excretory vesicle Y-shaped; arms united in fore; ; body. Parasitic usually in gut (normally stomach) of freshwater and marine teleosts, but occasionally recorded from amphibians, reptiles and freshwater shrimps. is a family which does not have a constant seminal storage and disposal apparatus female system. As discussed below (p. 124), the variations of this apparatus probably occur because they are a diverse and successful, but relatively primitive group, which appear to have evolved at about the time when the first modifications of the primitive arrangement of the seminal storage and disposal apparatus began to occur. The variety of conditions found in this group tend to parallel those which have occurred during the evolution of some of the more advanced hemi- COMMENT. This in the uroids, such as the hemiurids, bunocotylids Key 1 . to A. B. 2. A. Derogenidae and lecithasterids. ......... GONOCERCINAE Testes posterior to ovary and vitellarium (p. 74) 2 Testes anterior to ovary and vitellarium Parasites primarily of freshwater teleosts, but occasionally present in brackish water or marine teleosts close to the ancient Sarmatic Sea region [Caspian. Black and Mediterranean Seas], in amphibians, in reptiles and in freshwater shrimps; ventral sucker occasionally anterior to middle of body; uterus not present posterior to vitellarium; sinus-sac, when present, may enclose part of or entire seminal vesicle and/or pars HALIPEGINAE B. (p. 75) prostatica Parasitic in marine teleosts ventral sucker not present in anterior half of body uterus often extends posterior to vitellarium; sinus-sac present, never enclosing any part of pars (p. 71) prostatica or seminal vesicle ; ; DEROGENINAE Subfamily Liopyginae Ejsmont, Ejsmont, Genarchinae Skrjabin & Orthoruberinae Nasir & (?) (?) Liocercinae DEROGENINAE 1931 1931 Guschanskaja, 1955 Gomez, 1977 Nicoll, 1910 72 D. I. GIBSON & R. A. BRAY Ventral sucker in middle or posterior to middle of body. Gut-caeca end blindly or form cyclocoel. Testes pre-ovarian; symmetrical to oblique. Seminal vesicle small; globular to tubular. Pars prostatica usually tubular, occasionally vesicular; short or long. Sinus-sac present; globular to cylindrical. Permanent sinus-organ present; small; cone-shaped. Hermaphroditic duct normally short. Genital atrium small; often filled by sinus-organ. Ovary close behind testes. Laurer's canal present or absent; opening dorsally or into rudimentary Juel's organ; may be dilated proximally forming large rudimentary or functional canalicular seminal receptacle. Blind seminal receptacle present when Laurer's canal and uterine seminal receptacle absent; latter usually present. Uterus coiled throughout hindbody and part of forebody; significant proportion of uterus often present posterior to vitellarium. Eggs without filaments or threads, but may have anopercular spine. Vitellarium two symmetrical to tandem, oval or slightly indented masses posterior or occasionally and postero-lateral to ovary. Parasitic in gut (mainly stomach) of marine teleosts. ; lateral Key 1. 2. to Derogeninae A. Uterus not normally extending posterior to vitellarium B. Significant proportion of uterus posterior to vitellarium A. Cyclocoel present Gut-caeca end blindly B. ...... ...... ............ .... 4 2 PROGONUS 3 3. A. 4. A. DEROGENOIDES Eggs drawn into sharp point at anopercular pole DEROGENES Eggs lacking point at anopercular pole Vitelline masses tandem to oblique, lateral and postero-lateral to ovary; blind seminal B. Vitelline B. LEURODERA receptacle present masses symmetrical to oblique, post-ovarian; Laurer's canal and presumably GONOCERCELLA uterine seminal receptacle present COMMENT. Initially, we considered Gonocercella and Leurodera to be members of the Halipeginae because of the pre-vitelline distribution of the uterus. The fact that they parasitize marine teleosts and the structure of the terminal genitalia, however, clearly associated them with the Derogeninae. It could also be argued that Arnold, Magnibursatus and Tyrrhenia, which are present in teleosts from the brackish to marine conditions of the Black and Mediterranean Seas, should be included in the Derogeninae. The structure of the terminal genitalia, however, is different from that of the latter group. In addition, these three genera are morphologically related to some of the Asian halipegines from freshwater and can be historically and zoogeographically related to the halipegines of the central Asian region via the ancient Sarmatic Sea. DEROGENES Liihe, 1900 [n(w,s)] Liopyge Looss, 1899 (l)Liocerca Looss, 1902 (1) Gut-caeca end blindly near posterior extremity. Testes symmetrical to oblique. Seminal vesicle globular to tubular and sinuous. Pars prostatica short to long. Sinus-sac globular. Male and female ducts unite within sinus-organ. Ovary usually close behind testes; may be lateral to posterior testis when latter is oblique. In D. varicus Laurer's canal opens distally into rudimentary Juel's organ and dilates proximally forming large rudimentary seminal receptacle. Uterine seminal receptacle present. Uterine field usually extends from posterior extremity to region of genital pore; significant proportion of uterus posterior to vitellarium. Eggs without anopercular spine. Vitelline masses symmetrical to oblique; globular or slightly indented; post-ovarian. Parasitic in stomach, oesophagus or occasionally gall-bladder of marine ( ? and freshwater) teleosts. TYPE-SPECIES. Derogenes ruher Liihe, 1900 [by monotypy]. COMMENT. The overall morphology ofLiopyge bonnieri (Monticelli, 1893) is probably identical to that of Derogenes, if the vitellarium and the testes have been confused. It is difficult to believe, however, that an experienced worker like Monticelli would make such a mistake, especially as he originally considered his specimens to be Distoma varicum [now Derogenes varicus (Miiller, 1780)], and later re-named them Distoma bonnieri. Monticelli recorded this species from Trig/a THE HEMIUROIDEA 73 gurnardus in the English Channel. Evidence against the validity of the genus Liopyge is that in spite of the abundance of this host it has never been found a second time, although Derogenes various has been recorded from the English Channel in Trigla gurnardus by Nicoll (1914) and in T. lucerna by Nicoll (1914), Baylis & Jones (1933) and by ourselves: we have re-checked the determination of the last two records. Until there is more conclusive evidence for the existence of Liopyge, therefore, we are including this genus, and its synonym Liocerca, as questionable synonyms of Derogenes. The genus Pronopyge Looss, 1 899, has been considered to be a close relative of Liopyge (see Yamaguti, 1971). Its type-species was originally quoted as P. ocreata (Rudolphi, 1802); but Fasciola ocreata of Rudolphi (1802) was shown by Odhner (1911) to be a species of Hemiurus, and, as stated by Poche (1926), Pronopyge must be considered a junior synonym of the latter genus. Monticelli (1891) considered Distoma ventricosum Rudolphi, 1819 (and van Beneden, 1871) [nee D. ventricosum (Pallas, 1774)], and Distomum carolinae Stossich, 1889, to be synonyms of Fasciola ocreata Rudolphi, 1802. Figures of these two species by van Beneden (1871) and Stossich (1889) and of'Apoblema ocreata' by Monticelli (1891) suggest that they belong to the fellodistomid genus Pseudopentagramma Yamaguti, 1971 (a junior synonym of Pronoprymna Poche, 1926 see similar to of in and are & Gibson, Pseudopentagramma symmetrica figures prep.) they Bray (Chulkova, 1939) produced by Margolis & Ching (1965). DEROGENOIDES Nicoll, 1913 Gut-caeca end blindly. Testes symmetrical to oblique. Seminal vesicle small; globular. Pars somewhat cylindrical with proximal end slightly enlarged. Sinusorgan (?) presumably present. Ovary immediately posterior to testes. Laurer's canal and Juel's organ (?). Seminal receptacle (? rudimentary) reported. Uterine seminal receptacle (?). Much of uterus present posterior to vitellarium. Eggs drawn out to sharp point at anopercular pole. Vitelline masses entire; symmetrical; post-ovarian. Parasitic in stomach and intestine of marine prostatica short. Sinus-sac teleosts. TYPE-SPECIES. Derogenoides ovacutus Nicoll, 1913 [by original designation]. COMMENT. Derogenoides skrjabini Vlasenko, 1931, was made the type-species of Magnibursatus by Naidenova (1969). D. tetralecithum Roman, 1955, and possibly D. sargi Pogoreltseva, 1954, also appear to be halipegines. GONOCERCELLA Manter, 1940 Ventral sucker in posterior half of body. Gut-caeca end blindly. Testes oblique. Seminal vesicle tubular; coiled. Pars prostatica vesicular. Sinus-sac small. Sinus-organ a muscular cone. Ovary immediately posterior to testes; close to posterior extremity. Laurer's canal opens dorsally (according to MacCallum, 1913). Blind or canalicular seminal receptacle absent. Uterine seminal receptacle presumably present. Juel's organ presumably absent. Uterus mainly coiled in forebody not reaching posterior to vitellarium. Eggs without anopercular spine. Vitelline masses entire; ; symmetrical; post-ovarian; close to posterior extremity. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Gonocercella pacifica Manter, 1940 [by original designation]. LEURODERA Orthoruberus Nasir & Gomez, Union, 1910 [n(w)] 1977 Body oval; stout. Gut-caeca end blindly near posterior extremity. Testes symmetrical; largely or partly extra-caecal. Seminal vesicle tubular; slightly sinuous. Pars prostatica short; with few to many external gland-cells ; may be partly tubular and vesicular anteriorly. Sinus-sac oval. Sinusorgan small (well developed and conical in Orthoruberus}. Ovary just posterior to testes; close to posterior extremity. Laurer's canal, Juel's organ and uterine seminal receptacle apparently absent. 74 D. I. GIBSON & R. A. BRAY Blind seminal receptacle present; large; antero-ventral, antero-lateral or antero-dorsal to ovary. Uterus anterior to vitellarium; much of it pre-testicular. Eggs without anopercular spine. Vitelline masses entire or slightly indented; tandem to oblique; lateral and postero-lateral to ovary. Parasitic in gut (mainly stomach) of marine teleosts (especially Pomadasyidae). TYPE-SPECIES. Leurodera decora Linton, 1910 [by original designation]. & COMMENT. Leurodera ocyri Travassos, Teixeira de Freitas Blihrnheim, 1965, and L. inaequalis Teixeira de Freitas Buhrnheim, 1966, are not, in our opinion, specimens of Leurodera. Travassos, The descriptions appear to resemble Lecithophyllum and Aponurus, and Overstreet (1973) considered these two species to be synonyms of Aponurus pyriformis (Linton, 1910). & PROGONUS Looss, 1899 [t(w,s)] Genarches Looss, 1902 Cyclocoel present. Testes symmetrical. Seminal vesicle elongate, spindle-shaped, elongate oval or globular. Pars prostatica short; slightly vesicular. Sinus-sac small; globular. Ovary sinistral; halfway between testes and posterior extremity. Canalicular seminal receptacle present. Laurer's canal ends blindly after passing dorsally through cyclocoel. Rudimentary JueFs organ present as small dilations of Laurer's canal at distal extremity and especially at junction with seminal receptacle. Uterine seminal receptacle absent. Uterus extends posteriorly to vitellarium fills most of hindbody and some of forebody. Eggs without anopercular spine. Vitelline masses entire; symmetrical; post-ovarian. Parasitic in stomach of marine teleosts. ; TYPE-SPECIES. Progonus muelleri (Levinsen, 1881) [by original designation]. COMMENT. In agreement with Poche (1926) and Bray (in press), Progonus Looss, 1899, cannot be considered a junior homonym ofProgona Berg, 1 882 (Recommendation of Article 36, International Rules of Zoological Nomenclature, 1926; Article 56(a), International Code of Zoological Nomenclature, 1961). The apparent canalicular seminal receptacle present in this genus is essentially a type of blind seminal receptacle, especially as Laurer's canal does not open dorsally. The canalicular seminal receptacle (sensu stricto) is not found in the Hemiuroidea, except in the case of Trifoliovarium, and is normally associated with the use of Laurer's canal as a vagina during copulation (see Gibson & Bray, 1975). Subfamily GONOCERCINAE Skrjabin & Guschanskaja, 1955 Hemiperinae Yamaguti, 1958 Ventral sucker posterior to middle of body. Gut-caeca end blindly. Testes post-ovarian; tandem to symmetrical; near posterior extremity. Seminal vesicle usually small; oval to tubular; in forebody. Pars prostatica tubular; short; linked to seminal vesicle by short, aglandular duct. Sinussac absent or poorly developed. Sinus-organ absent or present as small, blunt cone. Hermaphroditic duct absent or short. Genital atrium small or apparently absent. Ovary between testes vitellarium. Laurer's canal present; opening dorsally; dilated proximally forming small rudimentary seminal receptacle. JueFs organ absent. Uterine seminal receptacle present. Uterus en- and tirely pre-ovarian; most of coils usually in forebody. Eggs filamented or not. Vitellarium two entire or indented, oval masses; symmetrical; antero- to postero-lateral to ovary. Parasitic in stomach or branchial cavity of marine Key 1. to teleosts. Gonocercinae A. Eggs without filaments; sinus-sac and sinus-organ absent (but see comment on Gonocerca) B. Eggs filamented; sinus-sac weakly developed; sinus-organ present. . . GONOCERCA HEMIPERA THE HEMIUROIDEA GONOCERCA 75 Manter, 1925 [t(w,s>] Ventral sucker in posterior half of body. Testes tandem to almost symmetrical; at posterior extremity of body. Seminal vesicle small; thin-walled; oval; close behind genital pore. Pars prostatica short; tubular. Sinus-sac and sinus-organ absent [see Comment]. Hermaphroditic duct absent (assuming that the small cavity into which male and female ducts open is the genital atrium). Genital atrium small or apparently absent. Ovary median. Uterus entirely pre-ovarian; largely in forebody. Eggs without filaments. Vitelline masses lateral or antero-lateral to ovary; entire to indented. Parasitic in stomach of marine teleosts (especially in mid-ocean). TYPE-SPECIES. Gonocerca phycidis Manter, 1925 [by monotypy]. COMMENT. Manter (1934) described G. phycidis and G. crassa with a genital papilla present in both, and Laurer's canal absent in the latter. Our sectioned material of G. phycidis indicates that a sinus-organ is absent and that a well-developed Laurer's canal is present (see Gibson, 1976: figs 14b and 14c). work there have also been conflicting opinions as to the presence of Laurer's canal in G. crassa, Yamaguti (19386) stating it to be present and Rees (1953) absent. Both Rees (1953) and Brinkmann (1975) agree that a small but distinct genital atrium and genital papilla Since Manter's are present in G. crassa. If this is so, this species can hardly be considered to be with the other species of the genus. In view of the great morphological variability of congeneric G. phycidis and the morphological similarity with Derogenes varicus, with which G. crassa has been recorded, we consider that any change in its taxonomic status should await a complete ^sinus-organ) redescription. HEMIPERA Nicoll, 1913 [t(w,s)] Hemiperina Manter, 1934 Ventral sucker in posterior half of body. Testes symmetrical to oblique at posterior extremity. Seminal vesicle oval to tubular. Pars prostatica tubular; short. Seminal vesicle and pars prostatica may apparently be enclosed by common, sub-globular, parenchymatous capsule. Sinus-sac weakly developed with diffuse musculature enclosing base of sinus-organ and proximal region of genital atrium. Sinus-organ a blunt cone. Male and female ducts may open separately on sinusorgan or form short hermaphroditic duct. Ovary median. Uterus entirely pre-ovarian; largely in forebody. Eggs filamented. Vitelline masses antero- to postero-lateral to ovary; entire or slightly indented. Parasitic in stomach or branchial cavity of marine teleosts. ; ; TYPE-SPECIES. Hemipera ovocaudata Nicoll, 1913 [by original designation]. Subfamily HALIPEGINAE Poche, 1926 Arnolinae Yamaguti, 1958 Monovitellinae Ataev, 1970 Ventral sucker usually near middle of body, occasionally more anterior or posterior. Gut-caeca end blindly or form cyclocoel. Testes pre-ovarian; symmetrical to oblique or occasionally tandem to oblique. Seminal vesicle globular to tubular; sometimes entirely or partly internal. Pars prostatica tubular to vesicular; normally short; sometimes internal. Sinus-sac present or absent; usually weakly developed may enclose pars prostatica and all or part of seminal vesicle. Sinusorgan present or absent; when present usually small, poorly developed and cone-shaped. Hermaphroditic duct usually short, occasionally long; rarely absent. Genital atrium small. Ovary usually close to posterior extremity. Laurer's canal present; with dorsal pore or short and leading ; into Juel's organ. Rudimentary seminal receptacle often present when Laurer's canal opens dorsally. Blind or canalicular seminal receptacle absent. Uterine seminal receptacle present. Uterus entirely or almost entirely anterior to vitellarium; coils extend into forebody, except in cases with ventral sucker inside anterior half of body. Eggs with or without filaments or threads. D. 76 I. GIBSON & R. A. BRAY Vitellarium one or two masses at posterior extremity of body; usually entire, but sometimes with normally in hindbody, occasionally in forebody. of freshwater teleosts; also recorded from brackish stomach) (normally gut Usually water and marine teleosts close to the ancient Sarmatic Sea region (Caspian, Black and Mediterranean Seas), amphibians, reptiles and freshwater shrimps (the majority of genera occur in Asia). indistinct or digitate lobes. Excretory bifurcation parasitic in COMMENT. Certain genera of halipegines are closely related, differing basically in the apparent filaments or threads on the eggs or in the degree of union between the two of or absence presence vitelline masses. One such group comprises Allotangiopsis, Chenia, Genarchopsis, Monovitella and Tangiopsis, all of which occur in central, southern and south-east Asia. Another such group is Arnold, Magnibursatus and possibly Anguillotrema and Tyrrhenia, which, with the exception of Anguillotrema from central China, come from the Black or Mediterranean Seas. There appear to be fundamental differences in the seminal disposal apparatus in the female reproductive system, as some genera possess Laurer's canal with a dorsal opening and others have a fully developed Juel's organ. The systematic significance of this must await further work, because the arrangement in most of the genera Key 1. to Halipeginae A. B. 2. A. B. 3. A. B. 4. A. B. 5. A. is as yet unknown. .......... ........... .4 .... .... .......... ......... 2 Eggs with filaments or threads Eggs without filaments or threads 8 Cyclocoel present Gut-caeca end blindly ALLOTANGIOPSIS Cyclocoel and excretory bifurcation in forebody GENARCHOPSIS Cyclocoel and excretory bifurcation in hindbody CHENIA Vitellarium a single mass 5 Vitellarium two similar masses Vitelline masses entire; sinus-sac completely enclosing pars prostatica and seminal vesicle; ventral sucker in anterior half of body; uterine coils retained in hindbody MA GNIBURSA TVS B. 6. A. B. 7. A. masses usually lobed; ventral sucker near middle of body or more posterior; 6 uterine coils extend into forebody 7 Vitelline masses lobed (usually with 4 and 5 small lobes) or occasionally entire THOMETREMA Vitelline masses with about 8 digitate extensions Sinus-sac encloses pars prostatica and entire seminal vesicle; vitelline masses lobed Vitelline ..... . . ANGUILLOTREMA 8. A. Sinus-sac usually weakly developed or (?) absent, sometimes enclosing prostatica glandcells, occasionally enclosing pars prostatica, rarely enclosing distal extremity of seminal HALIPEGUS vesicle; vitelline masses usually lobed, occasionally entire 10 Cyclocoel present; ventral sucker near middle of body; uterine coils extend into forebody B. Gut-caeca end blindly 9. A. Ventral sucker in anterior half of body; uterine coils retained in hindbody Ventral sucker near middle of body; uterine coils extend into forebody. Vitellarium a single mass B. . B. 10. A. B. Sinus-sac small, not enclosing pars prostatica and seminal vesicle. HALIPEGUS Looss, Dollfuschella & 1899 . . .... Vitellarium two similar masses situated close together Sinus-sac encloses pars prostatica and seminal vesicle Genarchella Travassos, Artigas Vitellotrema Guberlet, 1928 . 9 A. B. 11. . . . . . 11 TYRRHENIA MONOVITELLA TANGIOPSIS ARNOLA DEROPEGUS [t(w); n(w,s)] Pereira, 1928 Vercammen-Grandjean, 1960 Progenarchopsis Fischthal, 1976 Paravitellotrema Watson, 1976 Ventral sucker near middle of body. Gut-caeca end blindly. Testes symmetrical to slightly oblique. Seminal vesicle saccular. Pars prostatica short; often reduced. Sinus-sac usually weakly THE HEMIUROIDEA 77 developed or ( ?) absent often enclosing pars prostatica and, on some occasions, distal extremity of seminal vesicle. Temporary sinus-organ may be developed as conical papilla (may occasionally be permanent); on some occasions male and female ducts open separately through this papilla. Hermaphroditic duct, when present, short. Genital atrium normally small. Ovary usually separated from testes by uterus, but not always. Laurer's canal present, with dorsal pore; proximal region dilate forming rudimentary seminal receptacle. Juel's organ absent. Uterus not extending posteriorly to vitellarium; usually with about equal distribution in fore- and hindbodies. Eggs with long, single filament at anopercular pole. Vitellarium two relatively symmetrical masses; usually clearly four- and five-lobed, sometimes indistinctly lobed or entire. Parasitic in upper regions of gut (usually stomach) of freshwater teleosts, amphibians and reptiles; those from amphibians often recorded from mouth, one record from ear (Cosmopolitan). ; TYPE-SPECIES. Halipegus ovocaudatus (Vulpian, 1859) [by monotypy]. COMMENT. Our concept of Halipegus may be considered wide; but, until more of the constituent species have been carefully and critically described, we believe that this concept is the most useful. In particular there appears to be a need for careful descriptions of the terminal genitalia in this genus: that of the type-species, for instance, is poorly known. The vitellarium is rather variable, the paired masses being distinctly lobed in the type-species and in most other species in the genus, weakly or indistinctly lobed in some species [e.g. H. kessleri (Grebnitzky, 1872)] and entire in some species [e.g. (Travassos, Artigas H. [Vitellotrema] fusipora (Guberlet, 1928), H. [=Genarchella] parva & Pereira, 1928) and the two species of Paravitellotrema Watson, 1976]. Halipegus cryptorchis Mane-Garzon & Gascon, 1973, is morphologically similar to Deropegus, in anterior the rather position of the ventral sucker. It differs, however, in the eggs especially being filamented and that part of the uterus is coiled in the forebody. ALLO TANGIOPSIS Yamaguti, 1971 Ventral sucker in middle of body. Cyclocoel present in forebody. Testes symmetrical to oblique. Seminal vesicle tubular, stout, recurved. Pars prostatica short, tubular; not delimited. Sinus-sac forms muscular wall surrounding hermaphroditic duct (?). Sinus-organ absent (?). Laurer's canal and organ (?). Seminal receptacle reported [presumably either rudimentary type or Juel's Uterine seminal receptacle situated, at least partly, in distal region of uterus. Uterus not organ]. reaching posterior to vitellarium; significant proportion present in forebody. Eggs filamented. Vitellarium two lobed masses; slightly oblique; at posterior extremity. Excretory bifurcation in forebody. Parasitic in gonads of freshwater shrimps as (?) progenetic metacercaria (China). Juel's TYPE-SPECIES. Allotangiopsis shanghaiensis (Yeh COMMENT. This genus and & Wu, 1955) [by original designation]. similar to Tangiopsis, differing only in the presence of filamented eggs in the anterior positions of the cyclocoel and the excretory bifurcation. The latter differences is might be explained by the relatively caudal position of the ventral sucker, a characteristic of metacercariae. ANGUILLOTREMA Chin & Ku, 1974 Ventral sucker in posterior half of body. Gut-caeca end blindly. Testes symmetrical. Seminal vesicle tubular; coiled; internal. Pars prostatica vesicular; internal. Sinus-sac large; weakly muscled; enclosing pars prostatica and seminal vesicle. Sinus-organ muscular; conical. Laurer's canal and Juel's organ (?). Uterus entirely anterior to vitellarium; large proportion in forebody. Eggs with a filament at each end and small threads surrounding base of filament at one end. Vitellarium two masses with four and five lobes; symmetrical at posterior extremity. Parasitic in stomach of eels in freshwater (China). TYPE-SPECIES. Anguillotrema papillatum Chin & Ku, 1974 [by original designation]. 78 D. I. GIBSON & ARNOLA R. A. BRAY Strand, 1942 [t(w,s)] Arnoldia Vlasenko, 1931, nee Mayer-Eymar, 1887 Ventral sucker in anterior half of body. Gut-caeca end blindly close to posterior extremity. Testes oblique; separated by uterus. Seminal vesicle coiled, tubular; internal. Pars prostatica short, straight; internal. Sinus-sac enclosing seminal vesicle and pars prostatica plus metraterm distally. Permanent sinus-organ absent. Short hermaphroditic duct and genital atrium present. Ovary immediately posterior to hind testis. Short, dilate Laurer's canal, containing sperm, opens into well-developed Juel's organ. Uterine seminal receptacle present. Uterus entirely anterior to vitellarium; coils not extending into forebody. Eggs without filaments. Vitellarium two symmetrical masses; situated close together at posterior extremity; slightly indented, usually indicating three and four lobes. Parasitic in stomach of marine teleosts (Diplodus) in Black Sea and Adriatic Sea. TYPE-SPECIES. Arnold microcirrus (Vlasenko, 1931) [by original designation]. COMMENT. The low salinity of the Black Sea and the similarity between this genus and several in Central Asia and the Far East suggest that Arnola might be a relict from freshwater genera from the ancient Sarmatic Sea, which arose in the upper Miocene epoch, contained brackish water and extended from the Black Sea region easterly into Central Asia. Our finding Arnola in the Adriatic Sea in no way invalidates this hypothesis, as a connection between this region of the Mediterranean Sea and the Sarmatic Sea (then called the Karangat Sea) occurred briefly during the Pleistocene epoch [see Zenkevitch, 1947; Ekman, 1953; Miller, 1972]. This genus appears to be closely related to Magnibursatus, Anguillotrema and Tyrrhenia. CHENIA Hsu, 1954 Ventral sucker just posterior to middle of body. Gut-caeca terminate blindly at level of ovary. Testes oblique. Seminal vesicle a curved, elongate sac. Pars prostatica internal (?; see figure 1 of Hsu). Sinus-sac enclosing attenuated anterior portion of seminal vesicle and pars prostatica. Sinus-organ not reported. (?) Seminal receptacle (presumably either rudimentary or Juel's organ) reported. Uterus entirely pre-ovarian; coils extending into forebody. Eggs reniform; with two filaments at one pole. Vitellarium single compact mass at posterior extremity. Parasitic in gut of freshwater gobiid teleosts (China). TYPE-SPECIES. Chenia cheni Hsu, 1954 [by monotypy]. DEROPEGUS McCauley & Parahalipegus Wootton & Pratt, 1961 Powell, 1964 Ventral sucker in anterior half of body. Gut-caeca end blindly near posterior extremity. Testes tandem, oblique or symmetrical. Seminal vesicle saccular. Pars prostatica short; tubular to slightly vesicular; surrounded by dense layer of gland-cells. Sinus-sac apparently present, but weakly developed; small. Sinus-organ a muscular cone. Ovary usually separated from testes by loops of uterus. Laurer's canal present; apparently opening dorsally; slightly dilated proximally, forming a rudimentary seminal receptacle. Juel's organ presumably absent. Uterine coils not extending into forebody; one loop may reach posterior to vitellarium. Eggs without filaments. Vitellarium two symmetrical to oblique, entire or slightly lobed masses; close to posterior extremity. Parasitic in stomach of amphibians and teleosts in freshwater (North America). TYPE-SPECIES. Deropegus aspina (Ingles, 1936) [by original designation]. GENARCHOPSIS Ozaki, Ophiocorchis Srivastava, 1933 ?) Pseudogenarchopsis Yamaguti, 1971 ( 1925 THE HEMIUROIDEA 79 Ventral sucker in posterior half, or occasionally in middle, of body. Cyclocoel present in hindbody; oesophageal pouch often present. Testes usually oblique, occasionally symmetrical. Seminal vesicle tubular to elongate-saccular; coiled. Pars prostatica short; may be vesi- slightly cular. Sinus-sac not clearly described, but may be weakly developed and enclose pars prostatica and perhaps distal extremity of seminal vesicle. Sinus-organ a strongly muscular, blunt cone. and well posterior to testes. Laurer's canal opening into well-developed opening dorsally (?). Uterus entirely pre-ovarian; coils extending into forebody. Eggs with long, polar filament. Vitellarium two entire or indented masses at posterior extremity; symmetrical to oblique. Parasitic mainly in stomach of freshwater teleosts, but there are two records from amphibians and two probable accidental infestations of snakes (Southern Asia and Far East). Ovary usually sinistral Juel's organ, or apparently TYPE-SPECIES. Genarchopsis goppo Ozaki, 1925 [by original designation]. COMMENT. Genarchopsis thapari Gupta & Chakrabarti, 1967, from the intestine of a snake, is only from four immature worms, and it is probably a fish-parasite which has been ingested by the wrong host. Yamaguti (1971) erected the genus Pseudogenarchopsis for this species; known but his only apparent valid criterion for doing so is that this species is purported to have a cirrussac. As far as Ophiocorchis is concerned, this genus is said to differ from Genarchopsis in possessing an oesophageal pouch. Rai (1972) found this feature either present or absent in one species (G. goppo), and it cannot be considered a character of generic importance. A well-developed Juel's organ in G. punctati Agrawal, 1966, was described by Anjaneyulu and Madhavi Rao (1974); but Ozaki (1925) described G. goppo, the type-species, as having Laurer's canal which opened dorsally. It seems unlikely that species with such apparently different seminal and vitelline disposal apparatus could be congeneric, but more detailed infor- & (1967) mation is required on G. goppo and other species in this genus in order to resolve this problem. Both Rai (1972) and Pandey (1975) also note the presence of Laurer's canal in G. goppo, but neither of them states how it terminates. MAGNIBURSATUS Naidenova, 1969 Ventral sucker in anterior half of body. Gut-caeca end blindly close to posterior extremity. Testes oblique, in anterior hindbody. Seminal vesicle coiled, tubular; internal. Pars prostatica short, straight; internal. Sinus-sac enclosing seminal vesicle and pars prostatica, plus the metraterm distally; in forebody. Sinus-organ absent. Short hermaphroditic duct or genital atrium present. Laurer's canal ends blindly (? in Juel's organ). Uterine seminal receptacle present. Ovary near posterior extremity; separated from testes by uterus. Uterus entirely anterior to vitellarium; not extending into forebody. Eggs with several (? six to eight) filaments (? threads) at each end. Vitellarium two oblique to symmetrical masses; close together at posterior extremity. coils Parasitic in stomach of euryhaline or marine teleosts (Black Sea region). TYPE-SPECIES. Magnibursatus skrjabini (Vlasenko, 1931) [by original designation]. MONOVITELLA Ataev, 1970 Ventral sucker in middle of body. Cyclocoel present in hindbody. Testes symmetrical. Seminal vesicle saccular. Pars prostatica short; vesicular. Sinus-sac reported absent (figure suggests it might be present as weakly muscled, tubular jacket of hermaphroditic duct). Sinus-organ absent (?). Genital atrium short. Ovary lateral; apparently extra-caecal situated between right testis and vitellarium. Laurer's canal and Juel's organ (?). Uterus almost entirely anterior to vitellarium, but descending loop reaches close to posterior extremity; coils extend into forebody. Eggs not filamented. Vitellarium a single, entire mass; lateral; apparently extra-caecal between ovary and posterior extremity. Parasitic in intestine of brackish water teleosts (Caspian Sea). ; TYPE-SPECIES. Monovitella cyclointestina Ataev, 1970 [by original designation]. COMMENT. Monovitella, despite certain apparent differences, is remarkably similar to Tangiopsis, 80 D. I. GIBSON & R. A. BRAY both of which are reported from gobiid fishes. Future work might show the two to be synonymous. Chenia is also morphologically similar and reported from gobiid fishes. TANGIOPSIS Skrjabin & Guschanskaja, 1955 Ventral sucker in middle of body. Cyclocoel present; caeca unite anterior to testes. Testes symmetrical to oblique. Seminal vesicle tubular; recurved. Pars prostatica small; free in parenchyma (according to Tang, 1951; but his figure suggests that the prostatic glands may be delimited or that the duct is vesicular and he has omitted the external gland-cells). Sinus-sac apparently absent. (?). Ovary between right testis and vitellarium. Laurer's canal opens dorsally. Juel's organ presumably absent. Rudimentary seminal receptacle apparently present. Uterus not passing posterior to vitellarium; almost entirely pre-ovarian; coils extend into forebody apparently filled with spermatozoa throughout most of its length. Eggs without fila- Temporary sinus-organ may be present ; ments. Vitellarium two slightly indented, symmetrical masses close together at posterior extremity united by short duct. Parasitic in stomach of freshwater teleosts (China). ; ; TYPE-SPECIES. Tangiopsis chinensis (Tang, 1951) [by original designation]. COMMENT: This genus is similar to Monovitella. THOMETREMA Amato, 1968 Ventral sucker in middle of body. Gut-caeca end blindly near posterior extremity. Testes oblique to symmetrical; separated by loops of uterus. Seminal vesicle tubular; stout; attenuated anteriorly; recurved. Pars prostatica with narrow lumen; surrounded by dense, oval mass of gland-cells. Sinus-sac not reported, but possibly present surrounding long hermaphroditic duct (see figures of Szidat, 1954). Sinus-organ present as small papilla in base of oval genital atrium (not reported by Ovary near posterior extremity; separated from testes by many loops of uterus; may have slightly irregular outline. Laurer's canal and Juel's organ (?). Uterus entirely preovarian coils extending into forebody. Eggs with one polar filament. Vitellarium two symmetrical masses of about eight short, digitate lobes, which are irregularly expanded distally. Parasitic in stomach of freshwater teleosts (Plecostomus}, occasionally in estuarine conditions (South Amato, 1968). ; America). TYPE-SPECIES. Thometrema magnified (Szidat, 1954) n. comb. [syn. T. portoalegrensis 1968 - type by original designation]. Amato, COMMENT. This genus was erected for a new species, T. portoalegrensis, from Plecostomus commersoni in Brazil by Amato (1968). The species Gonocercella magnified was described by Szidat (1954) from the same host in the estuary of the River Plate and from Plecostomus plecostomus in a neighbouring locality to Amato's record. Szidat's description is identical to that of Amato, with the exception that he described and figured the terminal genitalia in more detail and did not observe the filament on the egg. Considering that there is no evidence that Szidat teased out the eggs or sectioned his specimens, we have little hesitation in synonymizing the two species, as the presence of filamented eggs is often difficult to ascertain in whole-mounts. TYRRHENIA* Paggi & Orecchia, 1975 Ventral sucker near middle of body. Gut-caeca end blindly near posterior extremity. Testes oblique. Seminal vesicle saccular, but attenuated distally; internal. Pars prostatica (?) short, Orecchia the prostatica cells empty into the hermaphroditic duct); tubular (according to Paggi internal. Sinus-sac enclosing entire seminal vesicle and pars prostatica, plus metraterm distally. & short. Genital atrium apparently absent (or rudimentary seminal receptacle. Juel's organ absent. Uterine Permanent sinus-organ absent. Hermaphroditic duct small). Laurer's canal present, with * Paggi & Orecchia (1974) first used this name in an abstract, but without an accompanying description. THE HEMIUROIDEA 81 seminal receptacle present. Ovary immediately posterior to hind testis. Uterine coils reach posand extend into forebody. Eggs without filaments. Vitellarium two entire, teriorly to vitellarium symmetrical masses; situated close together immediately posterior to ovary and close to posterior stomach and on gills of marine teleosts (Blennius) in Mediterranean extremity. Parasitic in (Tyrrhenian) Sea. & TYPE-SPECIES. Tyrrhenia blennii Paggi Orecchia, 1975 [by original designation]. Gupta & Kumari, 1970, Genus of uncertain position CHELATREMA gen. inq. This genus was erected in an abstract by Gupta & Kumari (1970) for a new species, C. smythi [type by monotypy], from the Indian freshwater fish Chela baccala. It is said to belong to the subfamily Arnolinae of the family Hemiuridae. The genus is unrecognizable from the brief definition given, and appears Family to have characters unusual, or DICTYSARCIDAE Skrjabin & unknown, in the Hemiuroidea. Guschanskaja, 1955 Cylindrorchiidae Poche, 1926 Aerobiotrematidae Yamaguti, 1958 Pelorohelminthidae Fischthal & Kuntz, 1964 Albulatrematidae Yamaguti, 1965 Tetrasteridae Oshmarin, 1965 Dollfustravassosiidae Teixeira de Freitas & Kohn, 1967 Body usually large; oval; stout or flattened. Ecsoma absent. Body-surface smooth. Oral and ventral suckers well developed; ventral sucker in anterior half of body. Pharynx well developed. Oesophagus short. 'Driisenmagen' normally present (?). Gut-caeca end blindly close to posterior extremity. Testes two; large; symmetrical; oval or elongate; pre-ovarian; just posterior to ventral sucker. Seminal vesicle tubular; in forebody. Pars prostatica tubular. Sinus-sac well developed, poorly developed or absent. Permanent sinus-organ absent (? or present as small papilla); temporary sinus-organ may form. Genital atrium small or absent. Hermaphroditic duct well developed or indistinguishable from genital atrium sometimes appears to be continuation of metraterm with ejaculatory duct entering laterally. Ovary oval or with four (or five) short or elongate lobes; normally separated from testes by loops of uterus. JuePs organ* and uterine seminal receptacle ; present. Laurer's canal and blind or canalicular seminal receptacle absent. Uterus almost entirely retained in hindbody; mainly pre-ovarian or with many loops in post-ovarian field. Eggs without filaments; may link together and form chains. Vitellarium with six to eight (usually seven, arranged three and four) oval to digitiform lobes, or with two lateral acinous groups of follicles or two compact multilobulate masses postero- to antero-lateral or posterior to ovary. Excretory arms united in forebody. Parasitic in swim-bladder of physostomatous teleosts in a marine ; environment. COMMENT: The almost unique niche of these parasites in the swim-bladder of physostomatous shared in the Hemiuroidea by the genus Isoparorchis. Although considered to be closely related to the members of the Dictysarcidae by many authors, the latter genus differs because it occurs in a freshwater teleost and possesses several primitive features, such as Laurer's canal, a tubular vitellarium and a well-developed, muscular sinus-organ. teleosts Key 1. to Dictysarcidae A. B. * is ........... Uterus mainly pre-ovarian Uterine field mainly post-ovarian Observed in Elongoparorchis (see Madhavi . & . CYLINDRORCHIINAE subfam. Rao, 1974) and Dictysarca (see Manter, 1947). 2 inq. (p. 83) D. 82 2. I. GIBSON & R. A. BRAY A. Ovary oval (entire or irregularly lobed); vitellarium two compact multilobulate masses or two acinous bunches of follicles; hermaphroditic duct indistinguishable from genital B. Ovary 4- (or 5-) lobed vitellarium 6-8 (usually duct distinguishable from genital atrium. DICTYSARCINAE atrium 7) digitiform to oval lobes ; Subfamily DICTYSARCINAE . . Skrjabin & . (p. 82) hermaphroditic ; ALBULATREMATINAE (p. 82) Guschanskaja, 1955 stout. Cuticular ridge may encircle mid-hindbody. Testes oval; entire or irregularly lobed. Sinus-sac and sinus-organ absent. Hermaphroditic duct indistinguishable from genital atrium; tubular; short. Ovary oval; entire or irregularly lobed; in posterior third of hindbody. Uterus mainly pre-ovarian, but some loops present in post-ovarian field. Vitellarium two compact Body multilobulate masses or two acinous bunches of follicles; antero- or postero-lateral to ovary. Usually parasitic in marine Key 1 . eels. to Dictysarcinae ........ A. Cuticular ridge encircling mid-hindbody absent ovary irregularly lobed vitellarium in two, DICTYSARCA compact, multilobulate masses B. Cuticular ridge encircling mid-hindbody present ; ovary unlobed vitellarium two groups of AEROBIOTREMA acinous follicles ; ; ; DICTYSARCA Linton, 1910 No cuticular ridge present encircling mid-hindbody. Testes irregularly lobed. Seminal vesicle sinuous. Pars prostatica well developed. Hermaphroditic duct appears to be continuation of metraterm, with ejaculatory duct entering laterally. Ovary large; irregularly lobed. Vitellarium two compact, multilobulate masses; and sea-horses (Hippocampus). antero-lateral to ovary. Parasitic in moray eels (Gymnothorax) TYPE-SPECIES. Dictysarca virens Linton, 1910 [by original designation]. AEROBIOTREMA Yamaguti, 1958 Cuticular ridge present encircling mid-hindbody. Testes entire. Seminal vesicle sigmoid. Pars Ovary small; entire. Vitellarium two acinous bunches of follicles; one anteroand one postero-lateral to ovary. Excretory arms with numerous anastomosing side branches, prostatica straight. mostly lying close to caeca. Parasitic in marine eels (Muraenesox). TYPE-SPECIES. Aerobiotrema muraenesocis Yamaguti, 1958 [by original designation]. Subfamily Pelorohelminthinae Fischthal & ALBULATREMATINAE Yamaguti, 1965 Kuntz, 1964 Tetrasterinae Oshmarin, 1965 Body flattened to stout. Testes large; oval or elongate. Sinus-sac present; well or poorly developed. Hermaphroditic duct distinguishable from genital atrium. Ovary four (or five) distinct, oval or elongate lobes; in middle or posterior half of hindbody. Uterus mainly pre-ovarian or extending throughout hindbody. Vitellarium seven (occasionally six or eight) digitiform to oval lobes; immediately posterior or postero-lateral to ovary. Parasitic in marine ( ? or brackish water) teleosts. Key to Albulatrematinae LA. Vitelline lobes, ovarian lobes and portion of uterus post-ovarian. ....... testes oval ; ovary in middle of hindbody significant pro; ALBULATREMA THE HEMIUROIDEA B. Vitelline lobes 83 and ovarian lobes digitiform; testes elongate; ovary well inside posterior most of uterus pre-ovarian ELONGOPARORCHIS half of hindbody; . ALBULATREMA . . . Yamaguti, 1965 Seminal vesicle tubular; narrow; convoluted [according to Yamaguti, is replaced by a vas deferens, the distal portion of which is strongly muscular, convoluted and enclosed by an apparently muscular capsule]. Pars prostatica sigmoid; delimited. Sinus-sac well developed; bulbous. Temporary sinus-organ may be present. Genital atrium absent or (?) small. Ovary in middle of hindbody; ovarian lobes oval. Uterus extends throughout hindbody, much of it post-ovarian. Vitelline lobes oval to pyriform. Parasitic in marine (? or brackish water) teleosts (Albuld). Body stout. Testes oval. 1965, the seminal vesicle TYPE-SPECIES. Albulatrema ovale Yamaguti, 1965 [by original designation]. ELONGOPARORCHIS Rao, 1961 [n(w)] & Pelorohelmins Fischthal Kuntz, 1964 Tet raster Oshmarin, 1965 Dollfustravassosius Teixeira de Freitas & Kohn, 1967 flattened to stout. Testes elongate. Seminal vesicle sinuous; may reach dorsally to ventral sucker. Pars prostatica short. Sinus-sac poorly developed; present only distally as vestige surrounding base of genital atrium. Sinus-organ a small papilla-like structure (? temporary). Body Hermaphroditic duct relatively long; formed as continuation of metraterm, with ejaculatory duct entering laterally. Genital atrium oval or elongate-oval. Ovary well inside posterior half of hindbody; ovarian lobes digitiform. Uterus mainly pre-ovarian. Eggs may be linked together forming chains. Vitelline lobes digitiform; with condensed follicular appearance. Parasitic especially in catfishes, such as Arius. TYPE-SPECIES. Elongopar orchis pneumatis Rao, 1961 [by original designation]. COMMENT. In some descriptions of species of this genus Mehlis' gland has been considered to be the ovary and the ovary to be anterior lobes of the vitellarium (see Fischthal & Kuntz, 1964a; Teixeira de Freitas & Kohn, 1967; Fischthal & Thomas, 1968; but cf. Yamaguti, 1971). Subfamily CYLINDRORCHIINAE Poche, 1926, status emend, (subfam. inq.) [Original description inadequate.] Body elongate-oval. Testes elongate. Terminal genitalia not just inside posterior half of hindbody. Uterus convoluted posterior known. Ovary small; oval; to ovary straight anterior to ovary. Vitellarium two clusters of small follicles ovary. Parasitic in marine (? or brackish water) teleosts (Tetrodori). ; CYLINDRORCHIS Southwell, ; antero-lateral to 1913, gen. inq. Defined as subfamily. TYPE-SPECIES. Cylindrorchis tenuicutis Southwell, 1913 [by original designation]. COMMENT. We have included of C. tenuicutis were obtained, is Cylindrorchis as a genus inquirendus because the original description inadequate. Southwell (1913) states: 'As only very few specimens of this parasite was found impossible to satisfactorily make out with certainty, the precise it am not certain that the following description is confused the uterus with the vitellarium, the vitellarium for the ovary and the ovary for Mehlis' gland or JueFs organ, then it is conceivable that he may have been dealing with immature specimens of Ehngoparorchis. therefore details of the reproductive system. I absolutely correct in every detail'. If Southwell had Theoretically, the oldest family-group name available in this family is Cylindrorchiidae Poche, 1926; but, due to the questionable validity of Cylindrorchis, we feel that it would be inadvisable, at this stage, to use this genus as the type-genus of the family. 84 D. Family I. GIBSON & R. A. HEMIURIDAE BRAY Looss, 1899 Lecithochiriidae Liihe, 1901 Dinuridae Looss, 1907 Elytrophallidae Skrjabin & Guschanskaja, 1954 Body usually small, but elongate. Ecsoma present, occasionally reduced or vestigial. Bodysurface smooth or with annular plications; the latter occasionally being serrate giving a scaley appearance. Presomatic pit or ventro-cervical groove occasionally present. Oral and ventral suckers well developed; usually close together. Pharynx well developed. Oesophagus usually normally present. Gut-caeca terminate blindly; usually within ecsoma. Testes two; tandem, oblique or symmetrical; pre-ovarian; in hindbody. Seminal vesicle tubular, saccular or constricted into portions; muscular or thin-walled; in fore- or hindbody. Pars prostatica of variable length; usually tubular, but occasionally vesicular; may be linked to seminal short. 'Driisenmagen' vesicle by aglandular duct. Ejaculatory duct, if present, usually short. Sinus-sac usually well developed, occasionally reduced or absent. Prostatic or ejaculatory vesicle occasionally present within sinus-sac. Hermaphroditic duct usually enclosed within sinus-sac. Permanent sinusorgan and genital atrium well developed, small or absent; temporary sinus-organ may form from hermaphroditic duct in some cases. Genital pore mid-ventral at level of oral sucker or pharynx. Ovary oval; usually entire; post-testicular. Mehlis' gland post-ovarian. Laurer's canal and canalicular or blind seminal receptacle absent. Juel's organ and uterine seminal receptacle present. Uterus coiled mainly in pre- and/or post-ovarian region of hindbody; few or no coils present in forebody; initially descending into or towards ecsoma and then ascending towards forebody. Eggs numerous; small; embryonated; rarely with a polar filament. Vitellarium varies between forms with seven tubular branches (three on one side of body, four on other) and forms with two distinct, oval masses; mainly post-ovarian. Excretory vesicle Y-shaped; arms united in forebody or not. Parasitic mainly in gut, especially stomach, of marine teleosts, occasionally present in gut of freshwater teleosts and lung of sea-snakes. Key 1. to A. Hemiuridae Ejaculatory (or prostatic) vesicle present within sinus-sac, occasionally partly external [this vesicle should not be confused with a pars prostatic which is also present] Ejaculatory (or prostatic) vesicle absent Long, convoluted hermaphroditic duct and thin-walled permanent sinus-organ present; seminal vesicle bipartite, anterior part muscular; vitellarium 2 irregularly oval masses ......... . B. 2. A. 2 . 4 GLOMERICIRRINAE (p. 3. 4. 90) B. Hermaphroditic duct A. tubular or saccular and partitioned, usually thin-walled; vitellarium 7 digitiform to oval lobes or with tendency to form 2 distinct, often lobed, lateral masses; ecsoma sometimes reduced or apparently absent Eggs with polar filament commonly parasitic under surface of liver B. Eggs without polar filaments; normally parasitic A. Sinus-sac absent or poorly developed, when present usually of 'open'-type; seminal vesicle entirely or mainly thin-walled, usually constricted into portions; ecsoma sometimes B. Sinus-sac present, usually well developed, occasionally small 5 Vitellarium 2 symmetrical to slightly oblique, entire or lobed masses 6 Vitellarium 7 distinct oval to tubular lobes 8 Seminal vesicle oval or bipartite, in fore- or hindbody; ecsoma well developed; parasitic in gut of marine teleosts 7 Seminal vesicle tubular, extending well into hindbody; ecsoma reduced; parasitic in lung of sea-snakes (p. 98) Body-surface smooth; seminal vesicle in forebody, oval, thick-walled; sinus-sac very small relatively straight; permanent sinus-organ absent; seminal .......... A. 6. A. B. B. 3 ; in gut . HYPOHEPATICOLINAE (p. 91) LECITHOCHIRIINAE (p. 91) ..... .... PLERURINAE poorly developed 5. vesicle (p. 95) ........ ........... PULMOVERMINAE 7. A. LETHADENINAE B. Body-surface with plications or 'scales'; seminal vesicle thin- or partly to entirely thick-walled in hindbody, oval or (p. 95) bipartite, HEMIURINAE (p. 85) THE HEMIUROIDEA 8. A. B. 85 Seminal vesicle with thick muscular wall, oval; permanent sinus-organ normally delicate and amuscular ELYTROPHALLINAE Seminal vesicle thin-walled and oval, tubular or constricted into portions; permanent sinus-organ large and muscular, reduced to small papilla or apparently absent DINURINAE Subfamily HEMIURINAE (p. 89) (p. 86) Looss, 1899 Ecsoma well developed. Body-surface plicated or 'scaley' (i.e. with crenulate plications). Presomatic pit absent. Testes tandem to oblique. Seminal vesicle thin-walled, or partially or slightly muscular; bipartite or oval; in hindbody. Pars prostatica tubular; long; gland-cells occasionally delimited by membrane. Sinus-sac present often tubular not enclosing prostatic vesicle. Permanent sinus-organ absent, but hermaphroditic duct may be protruded to form temporary sinusorgan. Genital atrium usually small, but variable in length. Ovary oval. Vitellarium composed of two distinct oval masses, but these may show slight tendency toward lobation in three and four style. Excretory arms united in forebody. Parasitic in stomach of marine teleosts. ; Key 1. 2. ; to Hemiurinae A. B. Seminal vesicle bipartite Seminal vesicle oval A. Plications B. Plications ............ HEMIURUS on body-surface normal on body-surface crenulate, giving 'scaley' appearance HEMIURUS Rudolphi, . . 2 PARAHEMIURUS ANAHEMIURUS 1809 [t(w,s); n(w, s)] Apoblema Dujardin, 1845 Pronopyge Looss, 1899 (see p. 73). Metahemiurus Skrjabin & Guschanskaja, 1954 Body-surface with normal plications. Seminal vesicle constricted into two portions (? occasionally one of which may have thick, muscular wall. three), TYPE-SPECIES. Hemiurus appendiculatus (Rudolphi, 1802) [by subsequent designation: Stiles & Hassall, 1898]. COMMENT. Two subgeneric names have been erected: Metahemiurus Skrjabin & Guschanskaja, 1954, based upon sucker-ratios, the extent of the surface plications and the length of the ecsoma; and Neohemiurus Slusarski, 1958, based upon the presence of plications on the ecsoma. The former features are either variable or only of specific value, and the latter feature, plications on the ecsoma, is extremely doubtful (see p. 48) and requires confirmation. Metahemiurus has been used at the generic level by Brinkmann (1975). ANAHEMIURUS Manter, Body-surface with 'scaley' appearance relatively thick, muscular (i.e. 1947 with crenulate plications). Seminal vesicle oval; with wall. TYPE-SPECIES. Anahemiurus microcercus Manter, 1947 [by original designation]. PARAHEMIURUS Vaz & Pereira, 1930 [t(w)] Body-surface with normal plications. Seminal vesicle oval; with muscular wall of variable thickness. TYPE-SPECIES. Parahemiurus merus (Linton, 1910) [syn. P. type by original designation]. parahemiwus Vaz & Pereira, 1930- 86 D. I. Subfamily GIBSON & R. A. DINURINAE BRAY Looss, 1907 Stomachicolinae Yamaguti, 1958 Ecsoma well developed ; occasionally large. Body surface plicated or ally striated). Presomatic pit absent. Testes symmetrical to vesicle thin- walled; oval to tubular; may be constricted into smooth (apparently occasion- tandem; usually oblique. Seminal two to four portions; in forebody, dorsal to ventral sucker or in hindbody. Pars prostatica tubular or vesicular; short or long; may be linked to seminal vesicle by aglandular duct. Sinus-sac present; small or large; usually oval; not enclosing a prostatic vesicle. Permanent sinus-organ large and muscular, reduced to small papilla or apparently absent. Genital atrium usually well developed; deep or shallow (often depending upon contraction). Ovary usually oval; occasionally reniform or lobed. Terminal portion of uterus may or may not form distinct vesicle just outside sinus-sac. Vitellarium normally seven tubular lobes three on one side, four on the other. Excretory arms united or not united in forebody. Normally parasitic in stomach of marine teleosts. ; Key 1. to Dinurinae A. Seminal vesicle usually (but not always) constricted into portions; permanent sinus-organ present, but occasionally reduced to small papilla (sectioning usually required); pars ... B. 2. A. B. 3. A. prostatica usually linked to seminal vesicle by distinct aglandular duct Seminal vesicle not constricted into portions; permanent sinus-organ usually apparently absent, but may be present as small papilla; pars prostatica not normally linked to seminal vesicle by distinct aglandular duct Body-surface with plications Body-surface without plications Pars prostatica long, may be sparsely surrounded by gland-cells; seminal vesicle ........ ........... .......... DINURUS trilocular A. B. Aglandular region of pars prostatica short; seminal A. Parasitic in ........... ... . A. B. 5. . ERILEPTURUS ventral sucker; sinus-sac usually dilate proximally vesicle in forebody; sinus-sac elongate oval 6. . B. A. .... . B. A. B. 9. A. B. by PARADINURUS PROSTERRHURUS . by MECODERUS long aglandular duct 8 Anterior part of hindbody with normal configuration; pars prostatica undivided 9 Ecsoma large; seminal vesicle oval or elongate-oval TUBULOVESICULA Ecsoma normal seminal vesicle tubular and sinuous ALLOSTOMACHICOLA Seminal vesicle in forebody STOMACHICOLA Seminal vesicle in hindbody . 8. ATHERIA teleosts; pars prostatica connected to seminal vesicle short aglandular duct; excretory arms not united in forebody Parasitic in intestine of freshwater teleosts (?) Anterior part of hindbody greatly attenuated; pars prostatica in two parts separated stomach of marine . 1. 3 4 Pars prostatica short, connected to seminal vesicle by long aglandular duct; seminal ECTENURUS vesicle variable, tubular, saccular or divided into 2 or 3 sections Glandular region of pars prostatica short; excretory arms unite in forebody; distal end 5 of uterus often vesicular 6 Glandular region of pars prostatica long; distal end of uterus not vesicular Aglandular region of pars prostatica long; seminal vesicle dorsal or postero-dorsal to B. 4. 2 . . .... ; . . . We considered separating this group into two, using the features in the first part of the of the functional association between the presence of a permanent sinus-organ and a because key, seminal vesicle constricted into sections by sphincter muscles (see p. 129). The two groups, COMMENT. however, appear to grade into one another. DINURUS Looss, Body-surface with plications. Seminal 1901 [n(w,s)] vesicle trilocular, or occasionally quadrilocular; in anterior hindbody or occasionally postero-dorsal to ventral sucker. Pars prostatica long; may be densely or sparsely invested by gland-cells; linked to seminal vesicle by aglandular duct. Sinus-sac and THE HEMIUROIDEA permanent sinus-organ present; of variable size. Ovary 87 oval. Excretory arms not united in forebody. TYPE-SPECIES. Dinurus tornatus (Rudolphi, 1819) [by original designation]. ALLOSTOMACHICOLA Yamaguti, 1958 Ecsoma enormous. Body-surface smooth. Seminal vesicle elongate-oval; in forebody. Pars prostatica short; vesicular [? or long, tubular; see fig. 13b of Chauhan, 1954]; not connected to seminal vesicle by distinct aglandular duct. Sinus-sac present; small; oval. Permanent sinusorgan apparently absent. Ovary reniform; may be indistinctly lobed. Majority of uterus within ecsoma; normally fills more than half of ecsoma. Excretory arms (?) united in forebody. TYPE-SPECIES. Allo stomachic ola secundus (Srivastava, 1937) [by original designation]. COMMENT. Stomachicola lepturusi Gupta & Gupta, 1976, appears to belong to ATHERIA this genus. Hafeezullah, 1975 Body-surface smooth. Seminal vesicle saccular; in forebody. Pars prostatica short, tubular; connected to seminal vesicle by short, aglandular duct. Sinus-sac present; elongate-oval. Permanent sinus-organ present; (?) long, muscular. Ovary oval. Distal extremity of uterus vesicular. Excretory arms united in forebody. TYPE-SPECIES. Atheria zakiae Hafeezullah, 1975 [by original designation]. COMMENT. This genus is apparently close to Erilepturus as a terminal dilation of the uterus occurs both genera, although it has not been reported in all species of Erilepturus. The differences in the shape of the sinus-sac and in the length of the aglandular part of the pars prostatica are of questionable generic importance in this case; but we provisionally accept this genus on the basis of the distinct difference in the position of the seminal vesicle. in ECTENURUS Looss, 1907 [t(w); n(w)] Magnacetabulum Yamaguti, 1934 Parectenurus Manter, 1947 Body-surface with plications. Seminal vesicle saccular, tubular or divided into two or three sections; postero-dorsal to ventral sucker or in anterior hindbody. Pars prostatica short (?or missing) connected to seminal vesicle by long, aglandular duct. Sinus-sac and permanent sinusorgan present; small. Ovary oval. Excretory arms not united in forebody. ; TYPE-SPECIES. Ectenurus lepidus Looss, 1907 [by original designation]. ERILEPTURUS Woolcock, Uterovesiculurus Skrjabin & 1935 [n(w)] Guschanskaja, 1954 Body-surface smooth (or finely transversely striated). Seminal vesicle variable; (?) oval, tubular same species dorsal or postero-dorsal to ventral sucker. Pars prostatica short, tubular; connected to seminal vesicle by long, aglandular duct. Sinus-sac present; dilate proximally (?or tubular). Permanent sinus-organ present; small. Ovary oval. Distal extremity of uterus (outside sinus-sac) may be vesicular. Excretory arms united in forebody. to trilocular in the ; TYPE-SPECIES. Erilepturus tiegsi Woolcock, 1935 [by original designation]. COMMENT. The vesicular nature of the terminal portion of the uterus, used by Skrjabin & Guschanskaja (1954) to erect Uterovesiculurus, is also found in Erilepturus platycephali (Yamaguti, 1934) whether according to Manter (1970), and possibly in other species of this genus. It is not clear this is a transient feature. In some species, such as those described by Yamaguti (1970), the proximal dilation of the sinus-sac is apparently missing. 88 D. I. GIBSON & R. A. BRAY MECODERUS Manter, 1940 Anterior part of hindbody attenuated. Body-surface smooth. Seminal vesicle saccular; well back in hindbody, just anterior to testes. Pars prostatica in two parts, one anterior to and other posterior to attenuated part of body, connected by long, aglandular duct; not connected to seminal vesicle by distinct aglandular duct. Sinus-sac present; small, oval. Permanent sinus-organ apparently absent. Ovary oval. Excretory arms united in forebody. TYPE-SPECIES. Mecoderus oligoplitis Manter, 1940 [by original designation]. COMMENT. There are certain morphological magna (Manter, 1931). similarities between PARADINURUSViguems, this genus and Stomachicola 1958 [t(w,s)] Body-surface smooth. Seminal vesicle trilocular; at level of ventral sucker. Pars prostatica tubular; long; densely invested with gland-cells; connected to seminal vesicle by short, aglandular duct. Sinus-sac oval; thick-walled; relatively large. Permanent sinus-organ well developed. Ovary oval. Excretory arms not united in forebody. TYPE-SPECIES. Paradinurus manteri Vigueras, 1958 [by original designation]. (1) PROSTERRHURUS Fischthal & Kuntz, 1963 Body-surface smooth. Seminal vesicle trilocular; in hindbody. Pars prostatica long, tubular; densely surrounded by gland-cells; apparently not linked to seminal vesicle by distinct, aglandular duct. Sinus-sac short; tubular. Permanent sinus-organ present; small. Ovary oval. Excretory arms ( ?). Parasitic in intestine of freshwater teleosts ( ? from estuarine region). TYPE-SPECIES. Prosterrhums labeonis Fischthal & Kuntz, 1963 [by monotypy]. COMMENT. The validity of this genus, which is based upon a single specimen, is questionable, because of shortcomings in its description and affinities with Erilepiurus. The details of the terminal genital apparatus are based upon figure 687 of Yamaguti (1971). According to Fischthal & Kuntz (1963), there is an elongate sinus-sac which encloses the distal ends of the pars prostatica plus the metraterm, a prostatic vesicle, an ejaculatory duct and the hermaphroditic duct. STOMACHICOLA & Pseudostomachicola Skrjabin Acerointestinecola Jahan, 1970 Indostomachicola Gupta & Yamaguti, 1934 Guschanskaja, 1954 Sharma, 1973 Ecsoma enormous. Body-surface smooth. Seminal vesicle oval; in hindbody. Pars prostatica not connected to seminal vesicle sinuous; tubular; long; by distinct aglandular duct; external gland-cells may not be evenly distributed throughout length. Sinus-sac present; small; oval. Permanent sinus-organ absent or reduced to rudiment. Ovary oval to reniform. Majority of uterine coils within ecsoma; normally fill less than half of ecsoma. Excretory arms united in forebody. TYPE-SPECIES. Stomachicola muraenesocis Yamaguti, 1934 [by original designation]. TUBULOVES1CULA Yamaguti, 1934 [n(s)] Lecithurus Pigulewsky, 1938 Body-surface smooth. Seminal vesicle tubular; sinuous; in hindbody. Pars prostatica with long, wide lumen; sinuous or straight; not connected to seminal vesicle by distinct aglandular duct. Sinus-sac present; oval. Permanent sinus-organ normally absent, but may occur as small papilla. THE HEMIUROIDEA Ovary oval 89 to round. Vitelline lobes tubular, but often stout. Excretory arms united in forebody. and body-tissues of marine teleosts (also reported from intestine Parasitic in stomach, body-cavity of sea-snake). TYPE-SPECIES. Tubulovesicula span' Yamaguti, 1934 [by original designation]. COMMENT. See Sinclair et al (1972) and Stunkard (1973) concerning Tubulovesicula v. Stomachicola. Several authors, such as Sogandares-Bernal (1959), consider T. lindbergi (Layman, 1930) to be a senior synonym of the type-species of this genus. ELYTROPHALLINAE Skrjabin & Guschanskaja, 1954 Subfamily Musculovesiculinae Ecsoma well developed. Body-surface cervical groove often present. Testes Skrjabin & Guschanskaja, 1954 smooth or plicated. Pre-somatic pit absent, but ventrotandem to symmetrical, usually oblique. Seminal vesicle with exceptionally thick, muscular wall oval, not constricted into portions present in forebody, dorsal to ventral sucker or in hindbody. Pars prostatica tubular; long or short; usually linked to seminal vesicle by short, aglandular duct. Sinus-sac present; commonly tubular, long; not enclosing ejaculatory or prostatic vesicle. Sinus-organ usually well developed, but delicate and ; ; amuscular. Genital atrium usually deep (depending upon contraction). Ovary oval. Eggs rarely filamented. Vitellarium seven tubular to tear-shaped lobes, three on one side, four on the other, which may form rosette. Excretory arms united in forebody. Parasitic mainly in stomach of marine Key 1. ........... .......... ...... to Elytrophallinae A. B. 2. A. 3. A. B. B. 4. teleosts. A. B. Body-surface with plications 2 Body-surface without plications 4 Glandular region of pars prostatica mainly in hindbody 3 Glandular region of pars prostatica in forebody CLUPENURUS Sinus-sac long and narrow, reaching to the level of the seminal vesicle; vitelline lobes tear-shaped ELYTROPHALLOIDES Sinus-sac relatively long, but not reaching to level of seminal vesicle; vitelline lobes tubular Seminal vesicle in forebody; eggs may be filamented MUSCULOVESICULA Seminal vesicle in hindbody; eggs not filamented ELYTROPHALLUS* .... . ELYTROPHALLUS Manter, . LEC1THOCLADWM . 1940 Body-surface smooth. Seminal vesicle small to large; in hindbody. Pars prostatica sinuous; mainly or entirely in hindbody. Sinus-sac long, tubular, thick-walled. Vitelline lobes tear-shaped to digitiform. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Elytrophallus mexicanus Manter, 1940 [by original designation]. (?) CLUPENURUS Srivastava, 1935 Body-surface with plications. Testes symmetrical to oblique. Seminal vesicle compact, oval; in hindbody. Pars prostatica in forebody. Sinus-sac bulbous; small. Vitelline lobes tubular. Parasitic in stomach of migratory clupeid teleosts (in freshwater). TYPE-SPECIES. Clupenurus piscicola Srivastava, 1935 [by original designation]. COMMENT. The taxonomy of the hemiurid parasites of Hilsa (=Clupea; =Ilisha) ilisha is confused, as the descriptions of the species recorded either contain questionable features or are totally * Joliniophylhnn is inadequately described, but keys to this position. 90 D. I. GIBSON & R. A. BRAY inadequate. In addition to Clupenurus piscicola, the following species of hemiurid have been re- corded from this host: Lecithocladium ilishae Mamaev, 1970, nee Bashirullah & D'Silva, 1973. Lecithocladium ilishae Bashirullah & D'Silva, 1973, nee Mamaev, 1970. Lecithocladium chauhani Hafeezullah, 1975. Some of these descriptions indicate relationships with the elytrophallines and others with the dinurines; but the problem cannot be resolved until a comparative study of these forms, some of which are probably synonymous, is undertaken. EL YTROPHALLOIDES Szidat, 1955 [T(w,s) ; t(w,s)] Body-surface with plications. Seminal vesicle large, reaching back to level of testes. Pars prostatica sinuous; in hindbody. Sinus-sac long, normally reaching back to level of seminal vesicle. Vitelline lobes tear-shaped. Parasitic in stomach of marine teleosts (in southern hemisphere). TYPE-SPECIES. Elytrophalloides oatesi (Leiper & Atkinson, 1914) [syn. E. merluccii Szidat, 1955 - type by original designation]. (l)JOHNIOPHYLLUMSkrjabm & Guschanskaja, 1954 [Inadequately described.] Body-surface smooth. Seminal vesicle small; in hindbody. Details of and pars prostatica not known. Vitelline lobes digitiform. Parasitic in intestine of marine sinus-sac teleosts. TYPE-SPECIES. Johniophyllum johnii (Yamaguti, 1938) [by original designation]. LECITHOCLADIUM Lime, 1901 [t(w); n(w,s)] Body-surface with plications. Oral sucker often funnel-shaped. Pharynx elongate. Seminal vesicle large; in hindbody. Pars prostatica long and sinuous; mainly or entirely in hindbody. Sinus-sac tubular; narrow; not reaching level of seminal vesicle and usually entirely or mainly in forebody. Vitelline lobes long and tubular. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Lecithocladium excisum (Rudolphi, 1819) [by original designation]. MUSCULOVESICULA Yamaguti, 1940 Body-surface smooth. Seminal vesicle elongate; in forebody or overlapping ventral sucker. Pars prostatica short and indistinct; in forebody. Sinus-sac elliptical to pyriform; short. Vitelline lobes digitiform. Eggs may be filamented. Parasitic in stomach of marine teleosts (eels). TYPE-SPECIES. Musculovesicula gymnothoracis Yamaguti, 1940 [by original designation]. Subfamily GLOMERICIRRINAE Yamaguti, 1958 Ecsoma well developed. Body-surface plicated. Pre-somatic pit absent. Testes oblique to tandem. Seminal vesicle bipartite; both parts globular to spindle-shaped; anterior part muscular; in hindbody or dorsal to ventral sucker. Pars prostatica tubular; short; linked to seminal vesicle by aglandular duct. Claviform sinus-sac present; in fore- or reaching into hindbody; enclosing prostatic vesicle. Hermaphroditic duct convoluted. Sinus-organ present; amuscular; long; convoluted. Genital atrium well developed. Vitellarium two irregularly oval, symmetrical masses. Excretory arms united in forebody. Parasitic in stomach of maiine teleosts. GLOMERICIRRUS Yamaguti, 1937 Defined as subfamily. TYPE-SPECIES. Glomericirrus amadai Yamaguti, 1937 [by original designation]. [n(w,s)] THE HEMIUROIDEA 91 COMMENT. The interpretation of the terminal genitalia, based on our own sectioned material, markedly from the early descriptions (Yamaguti, 1937, 1938b). The observations of Manter (1970) and Campbell & Munroe (1977) agree with our interpretation. differs Subfamily HYPOHEPATICOLINAE Skrjabin & Guschanskaja, 1954 Ecsoma reduced; appears to be permanently withdrawn. Body-surface Body spindle-shaped. smooth. Presomatic pit absent. Gut-caeca end blindly. Testes symmetrical at level of middle or posterior margin of ventral sucker. Seminal vesicle anterior or antero-dorsal to ventral sucker; two portions; elongate saccular; may be sinuous. Pars prostatica short; slightly linked to seminal vesicle by short, aglandular duct. Sinus-sac present; oval; be vesicular; may enclosing prostatic vesicle, part of metraterm and hermaphroditic duct. Permanent sinus-organ absent. Genital atrium present. Ovary oval. Much of uterus post-ovarian. Eggs with long, polar filament. Vitellarium seven digitiform lobes (three on one side, four on the other), forming postovarian rosette. Excretory arms united in forebody. Parasitic under connective tissue membrane of liver and in gut of marine teleosts. constricted into HYPOHEPATICOLA Yamaguti, 1934 [t(w)] Defined as subfamily. TYPE-SPECIES. Hypohepaticola callionymi Yamaguti, 1934 [by original designation]. COMMENT. This representative of a monospecific subfamily was originally found under the conmembrane of the liver, a very unusual habitat: it has also been recorded by Yamaguti (1942) from the stomach of the type-host, Callionymus valenciennesi, and from the nective tissue Monacanthus cirrhifer. Yamaguti states, The proper location of the worm may be the stomach of C. valenciennesi as is the case with one of the present examples, but in fact it occurs more frequently on the surface of the liver. M. cirrhifer may be an accidental host.' We have examined material from the liver of M, cirrhifer collected by Dr A. Ichihara from Sagami Bay, Japan, in 1966, and specimens were recorded from the liver of Callionymus flagris by Ichihara et al. (1963), so it appears that the liver is the normal site of this parasite. In our conception of Hypohepaticola, we have interpreted Yamaguti's (1934) 'distal portion of the pars prostatica' as being a prostatic vesicle and his 'small receptaculum seminalis' as being Juel's organ. In our view this genus is morphologically similar to the Lecithochiriinae, differing fundamentally according to the original description, only in the apparent absence of an ecsoma and the presence of filamented eggs. These two features are probably associated with the peculiar site of this parasite, as the presence of an ecsoma would not be significantly advantageous under the surface-membrane of the liver, whilst the presence of filaments on the eggs may aid their evacuation from the tissues of the host. When we examined specimens from M. cirrhifer we could with some difficulty distinguish a withdrawn ecsoma. There is no evidence that this small structure is ever extruded. This suggests intestine of that Hypohepaticola the reduction of the is closely related to the Lecithochiriinae, especially as there is a tendency for to occur in the latter group. For the present, however, we have ecsoma retained the subfamily Hypohepaticolinae, because of the unusual habitat and the filamented eggs. Hypohepaticola andamanensis Gupta Miglani, 1974, from 'a teleost marine fish' off India, appears, from the brief description given, to possess none of the definitive characters of this genus. & Their later (1976) description suggests that Subfamily Sterrhurinae Looss, 1907 Brachyphallinae Skrjabin Trithelaminae Yen, 1955 & it is LECITHOCHIRIINAE Guschanskaja, 1955 & a lecithasterid. Tricotyledoniinae Skrjabin Guschanskaja, 1957 Dissosaccinae Yamaguti, 1958 Liihe, 1901 D. 92 I. GIBSON & R. A. BRAY usually well developed, occasionally reduced. Body-surface usually smooth, but occasionand ventroally plicated or rugate. Muscular 'shoulder-pads' present or absent. Presomatic pit cervical groove present or absent. Testes tandem to symmetrical, usually oblique. Seminal vesicle elongate; constricted into two portions, which are occasionally separated by a duct, or tubular and convoluted; in bipartite forms anterior half may have thicker wall; normally in Ecsoma forebody, but forms with halves separated by duct may extend into hindbody. Pars prostatica short; vesicular or tubular; may extend slightly into base of sinus-sac; linked to seminal vesicle by short, aglandular duct. Sinus-sac present; rarely of 'open'-type; enclosing distinct ejaculatory or prostatic vesicle and metraterm. Permanent sinus-organ absent. Genital atrium usually small or absent, occasionally well developed. Ovary oval. Uterus mainly pre-ovarian or roughly equally distributed in pre- and post-ovarian fields. Eggs without filaments. Vitellarium seven digitiform to oval lobes in lateral groups of three and four, or with tendency to become two distinct lateral masses which often exhibit three and four lobes. Excretory arms united in forebody. Normally parasitic in gut of COMMENT. It is marine teleosts. important to distinguish a prostatic (or ejaculatory) vesicle from a vesicular pars some lecithochiriine and plerurine species become apparent. A prostatic (or ejaculatory) vesicle occurs entirely or mostly within a sinus-sac and together with a typical (external) pars prostatica from which it can be differentiated. In some prostatica, otherwise difficulties of distinguishing plerurine genera which possess a recognizable sinus-sac, e.g. Synaptobothrium, the pars prostatica extends into the base of the 'open' sinus-sac, but the region of the pars prostatica inside the sinus-sac is indistinguishable from the region outside. possibly divide the Lecithochiriinae into two groups: those with a distinctly seven-lobed vitellarium; and (2) those with a vitellarium composed of two entire or indistinctly lobed masses. We feel that the two groups do grade into one another, as the lobation in some species of Lecithochirium is reduced, whilst three- and four-lobed vitelline masses can be seen in some specimens of Brachyphallus. Some caution, therefore, should be One could (1) exercised Key 1. A. A. B. 3. the key presented below. to Lecithochiriinae B. 2. when using A. .... ......... .... .... 2 6 Vitellarium 7 distinct oval to digitiform lobes Vitellarium 2 entire masses which may be indistinctly 3- and 4-lobed Large, muscular 'shoulder-pads' present Large, muscular 'shoulder-pads' absent Small accessory sucker present anterior to oral sucker . . . 4 TRICOTYLEDON1A A. CYATHOLECITHOCHIRIUM No small accessory sucker CATARINATREMA Small muscular pad present anterior to oral sucker 5 Pre-oral lobe only present anterior to oral sucker PL1CATRWM Large, eversible genital atrium present LECITHOCHIRIUM Normal small genital atrium present Seminal vesicle composed of two parts separated by narrow duct and reaches into B. Seminal vesicle 7. A. Body-surface plicated anteriorly 8. A. B. 4. A. 5. A. B. B. 6. ....... . hindbody B. B. ... ............ . in . forebody, tubular or bipartite, parts not separated by a duct. . . . 8 PSEUDODINOSOMA smooth . Body-surface Seminal vesicle bipartite; body-surface plicated; deep presomatic pit DISSOSACCUS present BRACHYPHALLUS Seminal vesicle a wide, convoluted tube; body-surface smooth; presomatic pit absent; PROLECITHOCHIRIUM ecsoma reduced LECITHOCHIRIUM Luhe, Sterrhurus Looss, 1907 Ceratotrema Jones, 1933 Jajonetta Jones, 1933 Separogermiductus Skrjabin & Guschanskaja, 1955 1901 [t(w,s); n(w,s)] THE HEMIUROIDEA Magniscyphus Reid, Coil Neohysterolecitha 93 & Ahmad, Kuntz, 1965 1977 Ecsoma well or poorly developed. Body-surface smooth. Pre-oral lobe rarely with two lateral knobs. Presomatic pit and/or ventro-cervical groove often present. Seminal vesicle bipartite, tripartite or occasionally coiled; in forebody. Pars prostatica tubular, with wide lumen, to vesicular. Short, narrow extension of pars prostatica and/or ejaculatory duct may be present within sinus-sac. Ejaculatory (or prostatic) vesicle linked posteriorly to antero-dorsally with pars prostatica or ejaculatory duct. Temporary sinus-organ may form. Vitellarium two lateral masses; usually divided into three and four oval to digitiform lobes. Parasitic in gut (mainly stomach) of marine teleosts ; also recorded from body-cavity, hepatic ducts and gills of marine teleosts and (?) gut of freshwater reptiles. TYPE-SPECIES. Lecithochirium rufoviride (Rudolphi, 1819) [by original designation]. COMMENT. Sterrhurus is supposed to be distinguished from Lecithochirium by the absence of a presomatic pit (Lloyd, 1938; Manter & Pritchard, 1960a). The systematic significance of the presomatic pit has been discussed by Jones (1943) and Nasir & Diaz (1971). It appears to us that observations of this character have, in the past, not been careful enough. Many authors appear to have mistaken the ventro-cervical groove, which occurs commonly in this genus, for a presomatic pit, with the result that some descriptions must remain questionable. For example, Nahhas & Short (1965) described specimens of Lecithochirium mesosaccum Manter, 1947, from Sciaenops ocellata with a presomatic pit and from Synodus foetans without. If this character is to be taken as distinguishing these two genera, it would appear that specimens from Sciaenops are not Short representative of the same genus as those from Synodus. If we assume that Nahhas & mistook the ventro-cervical groove, a structure with a transitory nature, for a presomatic pit which is a permanent structure (see p. 49), then the specimens can be considered synonymous. We have examined the type-species of Lecithochirium and can confirm that a small [compared with that of Brachyphallus and Synaptobothrium] presomatic pit is present. This is visible in sections, but barely so in whole-mounts. We can also confirm that this structure is absent in Lecithochirium musculus (Looss, 1907), the type-species of Sterrhurus. Considering its small size in L. rufoviride and the questionable value of some of the information in the literature, we conit to be inadvisable at present to distinguish these two genera on this feature, although future work, involving the examination of many species in transverse sections, might show that it is a valid taxonomic criterion. Another feature used to distinguish Lecithochirium from Sterrhurus is the presence of a prostatic vesicle in the former and an ejaculatory vesicle in the latter (Crowcroft, 1946). The difference between these two types of vesicle is the presence of a lining of gland-cells in the case of the sider prostatic vesicle [we prefer to call the latter a glandular ejaculatory vesicle]. It appears, however, that these gland-cells can be lost, their concentration in one species varies and that they may in fact be present or absent in the same species (Manter & Pritchard, 1960a; Nasir & Diaz, 1971). This feature, therefore, appears to be of little value, except as an aid to specific identification. Contrary to the work of other authors, e.g. Jones (1943), in our sectioned material of L. rufoviride there are distal no gland-cells lining the ejaculatory vesicle; but, as in the case of L. musculus, the cells lining the pars prostatica do extend into the proximal extremity ends of some of the of the vesicle. Separogermiductus was distinguished from Lecithochirium in having 'a bulbous ejaculatory almost as large or even larger than the pharynx, lined with a refractive non-cellular wall, empty of cells or droplets, and into which the pars prostatica enters dorsally and anteriorly' (Manter & Pritchard, 1960a). We have had the opportunity of examining specimens of Lecithochirium genypteri Manter, 1954, which is considered by Manter & Pritchard (1960a) to be a species of Separogermiductus. The terminal genitalia are very much like those of our specimens of L. rufoviride. The ejaculatory vesicle is, perhaps, a little larger in L. genypteri, but the lining of the ejaculatory vesicle and the point of entry of the pars prostatica into this vesicle are very similar. In both cases the pars prostatica passes over the dorsal wall of the vesicle and enters vesicle, 94 D. I. GIBSON & R. A. BRAY antero-dorsally. As Jones (1943) shows the point of entry in L. rufoviride to be almost directly dorsal, it seems certain that this character varies to some extent, and is not reliable as a generic character. With regard to Magniscyphus, the 'cup- or bowl-shaped' forebody is merely a variation of the ventro-cervical groove, which is common in many species of Lecithochiriwn (according to our definition). Indeed, a similar condition can be seen in fig. 38 of Looss (1908), in which he figures The occurrence of so-called prostatic cells around the hermaphroditic duct requires histochemical confirmation, as this may have been a case of the misinterpretation of the small gland-cells which commonly occur within the sinus-sac of hemiuroids. If these cells are prostatic, then it is more likely that they are associated with the distal extremity of the pars prostatica, which occasionally extends into the base of the sinus-sac. We do not consider that the presence L. musculus. reason to substantiate the existence of Magniscyphus as a distinct genus their useful work on Lecithochirium, Nasir & Diaz (1971), in addition to including Sterrhurus, Separogermiductus and Magniscyphus as synonyms of Lecithochirium, also considered Synaptobothrium and Plerurus likewise. We believe that Nasir & of these cells is sufficient from Sterrhurus, and hence Lecithochiriwn. In Diaz (1971) went too far with their synonymies, and that Synaptobothrium and Plerurus are valid genera. BRA CH YPHALL US Odhner, 1 905 [t(w,s)] Body-surface plicated; plications may be crenulate. Presomatic pit present circular or oval; deep; Seminal vesicle bipartite; anterior part small, posterior part large; thin-walled; occurring mostly in forebody. Pars prostatica tubular. Temporary sinus-organ may be seen. Vitellarium two lateral masses; entire, irregularly lobed or indistinctly three- and four-lobed. ; glandular. Parasitic in gut (stomach) of marine and migratory teleosts. TYPE-SPECIES. Brachyphallus crenatus (Rudolphi, 1802) [by original designation], COMMENT. The terminal genitalia were described in detail by Lander (1904) and Slusarski and we agree that a glandular ejaculatory (prostatic) vesicle is present. CATAR1NATREMA Teixeira de Freitas & (1958), Santos, 1971 May bear papillae on ecsoma. Presomatic pit present. Muscular pad present anterior to oral sucker. Seminal vesicle bipartite; in forebody. Pars prostatica tubular. Vitellarium two masses of three and four short, digitiform lobes. Parasitic in stomach and intestine of marine teleosts. TYPE-SPECIES. Catarinatrema verrucosum Teixeira de Freitas & Santos, 1971 [by original designation]. CYATHOLECITHOCHIRIUM Yamaguti, 1970 sucker absent. Body-surface smooth. Muscular 'shoulder-pads' present. Pre-oral accessory Pars in thick Seminal vesicle bipartite; anterior part with wall; prostatica may be partly forebody. and four. Parasitic in of three in two lobes seven Vitellarium sinus-sac. within groups digitiform stomach of marine teleosts. TYPE-SPECIES. Cyatholecithochirium gymnothoracis Yamaguti, 1970 [by original designation]. DISSOSACCUS Manter, 1947 well developed. Body-surface smooth. Seminal vesicle in two parts separated by narrow to ventral sucker. Pars one duct; part normally mainly anterior and other mainly posterior Parasitic in stomach of marine masses. indented two Vitellarium tubular. slightly (?) Ecsoma prostatica teleosts. TYPE-SPECIES. Dissosaccus laevis (Linton, 1898) [by original designation]. THE HEMIUROIDEA PLIC ATRIUM Manter & 95 Pritchard, 1960 Papillae may occur on body-surface. Presomatic pit absent. Seminal vesicle bipartite; in forebody. Pars prostatica tubular. Large, eversible genital atrium present; wrinkled or convoluted when everted. Vitellarium seven digitiform lobes. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Plicatrium lycodontis (Myers & Wolfgang, 1953) [by monotypy]. PROLECITHOCH1RWM Yamaguti, 1970 Ecsoma reduced. Body-surface smooth. Presomatic pit absent. Seminal vesicle tubular convoluted ; and widening posteriorly; in forebody. Pars prostatica tubular. Vitellarium two compact masses. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Prolecithochirium pterois Yamaguti, 1970 [by original designation]. COMMENT. This genus has many of the characteristics of Lecithochirium ; but apparently lacks lobation of the vitellarium. PSEUDOD1NOSOMA Yamaguti, 1970 Ecsoma well developed. Body-surface with crenulate plications (? giving 'scaley' appearance). Presomatic pit absent. Seminal vesicle in two parts separated by narrow duct; one part (convoluted) anterior and other (claviform) posterior to ventral sucker. Pars prostatica tubular. Vitellarium two slightly indented masses. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Pseudodinosoma macrorchis Yamaguti, 1970 [by original designation]. TRICOTYLEDONIA Fyfe, 1954 [n(w,s)] Grassitrema Yeh, 1955 Body-surface smooth. Muscular 'shoulder-pads' present. Presomatic pit absent. Pre-oral accessory sucker present. Seminal vesicle bipartite; posterior part elongate; anterior to posterior margin of ventral sucker. Pars prostatica vesicular; partly enclosed by sinus-sac; leads into small, aglandular ejaculatory vesicle; connected to seminal vesicle by short, aglandular duct. Vitellarium seven digitiform lobes. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Tricotyledonia genypteri Fyfe, 1954 [by original designation]. Subfamily LETHADENINAE Yamaguti, 1971 Ecsoma well developed. Body-surface smooth. Pre-somatic pit absent. Testes oblique. Seminal vesicle oval; thick-walled; in forebody. Pars prostatica vesicular; with muscular wall; external gland-cells absent or weakly developed; separated from seminal vesicle by aglandular duct and from sinus-sac by long ejaculatory duct. Sinus-sac small; not containing ejaculatory or prostatic vesicle. Sinus-organ (?) present (? temporary) small. Genital atrium short. Vitellarium two symmetrical, unlobed, oval masses. Excretory arms not united in forebody. Parasitic in stomach of marine teleosts. ; LETHADENA Manter, 1947 Defined as subfamily. TYPE-SPECIES. Lethadena profunda (Manter, 1934) [by original designation]. PLERURINAE subfam. nov. Body small; spindle-shaped to cylindrical. Ecsoma reduced or well developed. Body-surface smooth, or occasionally with crenulate plications giving a scaley appearance. Presomatic pit 96 D. I. GIBSON & R. A. BRAY absent, except in Synaptobothrium. Prepharynx absent. Pharynx well developed. Oesophagus short. 'Driisenmagen' present. Gut-caeca terminate blindly inside ecsoma. Testes pre-ovarian; symmetrical to tandem, usually oblique. Seminal vesicle elongate, saccular and constricted into two, three or four sections; thin-walled, although certain sections may have thicker walls; in forebody or partly in hindbody. Pars prostatica vesicular or tubular; may be partly enclosed by muscles of sinus-sac; commonly linked to seminal vesicle by aglandular duct. Sinus-sac apparently absent or poorly developed; when present usually of 'open'-type. Permanent sinus-organ absent. Ejaculatory (prostatic) vesicle absent. Hermaphroditic duct commonly vesicular proximally and tubular distally. Genital atrium usually deep, but may be shallow. Genital pore mid-ventral in forebody. Ovary entire or lobed. Laurer's canal absent. Canalicular and blind seminal receptacles absent. Juel's organ present. Uterine seminal receptacle present. Uterus convoluted; passing back from ovary into ecsoma and then forward into forebody. Vitellarium post-ovarian; composed of two, four- and three-lobed, masses; the lobes being small to digitiform. Excretory vesicle Yshaped arms united in forebody. Parasitic in stomach of marine teleosts. ; important, in this group, to distinguish between a vesicular pars prostatica and an An ejaculatory vesicle occurs in the Lecithochiriinae, lacks external prostatic cells, is normally entirely enclosed within a distinct sinus-sac, and is present together with a normal pars prostatica which occurs externally to, or occasionally partly within, the COMMENT. It is ejaculatory (prostatic) vesicle. sinus-sac. The vesicular pars prostatica of the Plerurinae varies from being completely outside the by the muscles of a weakly developed sinus-sac, if it is present, to being only partly enclosed sinus-sac of the 'open'-type. Key 1. to Plerurinae A. Seminal vesicle tripartite in forebody, anterior and middle sections with thick, muscular VOITREMA wall A. Seminal vesicle saccular to 4-lobed or tubular, thin-walled Seminal vesicle in forebody Seminal vesicle at least partly extended into hindbody Presomatic pit absent; vitelline lobes digitiform Presomatic pit present; vitelline lobes short Body-surface has 'scaley' appearance B. Body-surface smooth B. 2. A. B. 3. A. B. 4. ...... ..... .... . PLERURUS Looss, 2 3 4 PLERURUS SYNAPTOBOTHRIUM DINOSOMA ADINOSOMA 1907 [t(w,s)] Paraplerurns Fischthal & Kuntz, 1963 Merlucciotrema Yamaguti, 1971 Ecsoma reduced or well developed. Body-surface smooth. Testes symmetrical to oblique. Seminal saccular, two-, three- or four-lobed; often sigmoid; thin-walled. Pars prostatica vesicular; may be linked to seminal vesicle by short aglandular duct (some authors maintain that this is a tubular region of the pars prostatica). Sinus-sac apparently absent or poorly vesicle in forebody; elongate; developed and of 'open'-type. Hermaphroditic duct tubular; deep; possibly eversible. to lobed. Vitelline lobes tubular to digitiform. Ovary oval TYPE-SPECIES. Plerurus digitatus (Looss, 1899) [by original designation]. COMMENT. Yamaguti (1970) points out that Looss (1908) figures a large oval seminal receptacle and suggests that what Looss actually saw was a uterine seminal receptacle. in the type-species, We confirm that a uterine seminal receptacle does occur in this species. Juel's organ has been Rao (1974) and we have observed described in P. longicaudatus (Yamaguti, 1953) by Madhavi it in the type-species. Owing to its close phylogenetic relationship (see Fig. 9) with the Lecithochiriinae, we wondered & whether the vesicular modification of the ejaculatory duct in this group might be a prostatic than a vesicular pars prostatica. Our observations of the type-species of this genus indicate that the structure present is a vesicular pars prostatica (see definition; p. 48). This is vesicle rather THE HEMIUROIDEA 97 not really surprising, if our suggestions as to its possible function are correct, because in the absence of a sinus-sac, there is no functional requirement for a prostatic vesicle. We have included Merlucciotrema, which Yamaguti (1971) based upon Manter's specimen of Sterrhurus praeclarus Manter, 1934, as a synonym ofPlerurus, because it appears to differ only in the reduced nature of the ecsoma and in that the vitelline lobes appear to be separated by narrow vitelline ducts. The size of the ecsoma is a variable feature in many hemiurid genera, even when contraction is taken into account, and Manter's original illustration suggests some evidence that the ecsoma of this species might be invaginated further than he indicates. ADINOSOMA Manter, 1947 Body-surface smooth. Testes oblique. Seminal vesicle large, saccular, bipartite; postero-dorsal to ventral sucker. Pars prostatica vesicular, but elongate; connected to seminal vesicle by long, aglandular duct. Sinus-sac apparently absent. Hermaphroditic duct long, with poorly developed hermaphroditic vesicle proximally. Ovary unlobed. Vitellarium two indented or lobed masses. TYPE-SPECIES. Adinosoma robustum (Manter, 1934) [by original designation]. COMMENT. This genus includes A. hawaiiense (Yamaguti, 1970) n. comb., a species which was originally placed in the genus Dinosoma. DINOSOMA Manter, 1934 [T(w,s); n(w,s)] Body-surface with crenulate plications, giving 'scaley' appearance. Testes symmetrical to tandem. Seminal vesicle postero-dorsal to ventral sucker; saccular, bipartite or wide; sinuous. Pars prostatica vesicular; may be connected to seminal vesicle by long, aglandular duct. Sinus-sac apparently absent. Hermaphroditic duct long, narrow; with small vesicle proximally. Ovary oval. Vitellarium two indented or lobed masses. TYPE-SPECIES Dinosoma rubrum Manter, 1934 [by original designation]. SYNAPTOBOTHRIUMvonLinstow, 1904 [t(w,s)] Body-surface smooth. Presomatic pit present; circular or oval; deep; glandular. Testes oblique. Seminal vesicle bipartite (? or tripartite); anterior part small, posterior part long; thin-walled; occurring mostly in forebody, but may extend dorsal to ventral sucker. Pars prostatica tubular with wide lumen; may extend into base of sinus-sac. Sinus-sac weakly developed; of 'open'-type. Ovary oval. Vitellarium two lateral masses with three and four short lobes. Eggs may be reniform. TYPE-SPECIES. Synaptobothrium caudiporum (Rudolphi, 1819) [syn. S. copulans von Linstow, 1904 - type by monotypy]. sinus-sac in this genus is weakly developed and of the 'open'-type, and an ejaculahave, therefore, included it in the Plerurinae. The wide pars tory (prostatic) vesicle is absent. prostatica may extend into the base of the 'open' sinus-sac. Lecithochirium apharei Yamaguti, COMMENT. The We 1970, probably belongs to this genus. (?) VOITREMA Yamaguti, 1971 [Inadequately known.] Body-surface (?). Testes oblique. Seminal vesicle tripartite; in forebody; and middle sections with thick, muscular wall. Pars prostatica vesicular; may be partly anterior enclosed by muscles of (?) sinus-sac; attached to seminal vesicle by short (?) aglandular duct. Sinus-sac (?) weakly developed; with diffuse musculature; of 'open'-type. Genital atrium sac-like. Ovary elongate oval. Vitelline lobes digitiform. TYPE-SPECIES. Voitrema COMMENT. This is amplum (Manter, 1961) [by original designation]. a questionable genus based upon one inadequately described specimen. D. 98 Subfamily I. GIBSON & R. A. BRAY PULMOVERMINAE Sandars, 1961 reduced. Body-surface smooth (? spines reported within suckers). Presomatic pit absent. to oblique. Seminal vesicle tubular; long; thick- walled; reaches to or almost to level of testes. Pars prostatica short; vesicular; partly enclosed by sinus-sac. Sinus-sac present; not enclosing ejaculatory or prostatic vesicle. Sinus-organ variable in length, (? temporary). Ecsoma Testes tandem Genital atrium small. Ovary occasionally divided into dorsal and ventral lobes. Vitellarium two masses; normally with three and four lobes. Excretory arms united in forebody. Parasitic in lung of sea-snakes. lateral, closely aligned PULMOVERMIS Coil & Kuntz, 1960 Hydrophitrema Sandars, 1960 Laticaudatrema Telford, 1967 Defined as subfamily. TYPE-SPECIES. Pulmovermis cyanovitellosus Coil Family & Kuntz, 1960 [by original designation]. HIRUDINELLIDAE Dollfus, 1932 Botulidae Guiart, 1938 Lampritrematidae Yamaguti, 1940 Mediolecithidae Oshmarin, 1968 [Includes: Profundiellinae Skrjabin, 1958] large; stout or elongate; contractile. Ecsoma absent. Body-surface smooth; may be papillate forebody or wrinkled. Oral and ventral suckers well developed; latter in anterior half of body. Pharynx well developed. Oesophagus usually short. 'Driisenmagen' present. Gut-caeca terminate blindly or form uroproct; sometimes fuse subterminally forming cyclocoel; usually diverticulate. Testes two; in tandem, oblique or symmetrical; pre-ovarian; in hindbody. Seminal vesicle tubular; normally thin- walled, occasionally partly thick- walled convoluted in forebody. Pars prostatica well developed; tubular; usually long. Ejaculatory duct long; muscular; surrounded by muscular 'cirrus-sac' opens into genital atrium through well-developed conical to cylindrical 'cirrus'. Hermaphroditic duct, sinus-sac and sinus-organ absent. Genital atrium large; usually Body in ; ; capable of being everted. Genital pore mid-ventral in forebody. Ovary oval; post-testicular; in middle or anterior half of hindbody. Laurer's canal and uterine seminal receptacle normally present. JuePs organ and blind or canalicular seminal receptacle absent. Uterus descending ventrally and ascending more dorsally; coiled mainly at level of vitellarium, but often extending more anteriorly into pre-ovarian region; mainly inter-caecal, occasionally reaching extra-caecally; metraterm opens into genital atrium directly or through a papilla-like organ situated immediately posterior to 'cirrus'. Eggs numerous; small; without filaments. Vitellarium composed of from two to numerous long, straight or convoluted, branched tubules mainly post-ovarian inter- or ; ; extra-caecal. Excretory vesicle Y-shaped; arms initially dorso-ventrally oriented, convoluted, united in forebody. Parasitic in stomach (occasionally on gills) of large, carnivorous, marine teleosts. COMMENT. In our opinion this family contains three monotypic genera which cannot be distinguished at the subfamily level. It is possible that Distoma gigas Nardo, 1827, from the stomach of Luvarus imperialis is a fourth genus; but, as suggested by Gibson Bray (1977), there is some evidence that this species may be a sclerodistomid (see p. 113). & Key 1. to Hirudinellidae A. B. ......... stout, elongate or keyhole-shaped; uroproct present; 'cirrus-sac' small, globular; seminal vesicle entirely thin-walled Body slender, elongate; uroproct absent; 'cirrus-sac' large, elongate; distal part of seminal Body vesicle with muscular wall 2 LAMPRITREMA THE HEMIUROIDEA 2. 99 ..... A. Vitellarium in two lateral fields between levels of testes and mid-hindbody; uterus mainly HIRUDINELLA inter-caecal, post-ovarian, at level of vitellarium B. Vitellarium massed close to ventral surface, inter-caecal between ovary extremity; uterus reaching extra-caecally, mainly in anterior hindbody HIRUDINELLA and posterior . . de Blainville, 1828 BOTULUS [t(w,s)] Hirudinella Garcin, 1730 [Pre-Linnaean; see Gibson, 1976] Uroproctinella Skrjabin & Guschanskaja, 1957 Body-surface often transversely wrinkled. Uroproct in older specimens forming cyclocoel. Testes symfuse sub-terminally present; gut-caeca may metrical to oblique; in anterior hindbody. Seminal vesicle thin-walled throughout its length. Body stout, elongate or keyhole-shaped. 'Cirrus-sac' relatively small; globular. 'Cirrus' cone-shaped to digitiform. Genital atrium capable of being everted through genital pore. Ovary in anterior hindbody. Uterus mainly inter-caecal; coils extending posteriorly from ovary to near posterior limit of vitellarium. Vitellarium in two between testes and middle of hindbody. Parasitic in stomach of large carnivorous, lateral fields marine teleosts (usually scombroids). TYPE-SPECIES. Hirudinella ventricosa (Pallas, 1774) [syn. H. clavata (Menzies, 1791) -type by monotypy]. COMMENT. As discussed by Gibson (1976), it is BOTULUS likely that this genus is monotypic. Guiart, 1938 [T(w,s); t(w,s)] Profundiella A. S. Skrjabin, 1958 Mediolecithus Oshmarin, 1968 stout. Uroproct present. Testes symmetrical to oblique; in anterior hindbody; thin-walled throughout its length; tubular and convoluted [or (?) globular Seminal vesicle large. (in Profundiella skrjabini A. S. Skrjabin, 1958)]. 'Cirrus-sac' small; globular. 'Cirrus' cone-shaped to digitiform. Genital atrium often everted through genital pore. Ovary in anterior hindbody. Uterus reaching extra-caecally in anterior hindbody. Vitellarium a densely tangled mass of tubeles in one ventral, inter-caecal field between ovary and posterior extremity. Parasitic in stomach of large, carnivorous, marine teleosts (Alepisaurus) and (?) accidentally in piscivorous Body normally sharks. TYPE-SPECIES. Botulus microporus (Monticelli, 1889) [syn. B. alepidosauri Guiart, 1938 -type by monotypy]. COMMENT. The two specimens of Botulus alepidosauri originally described by Guiart (1938), according to his manuscript, were in poor condition (they were dried out) which accounts for the inadequate description. We have been able to examine specimens of Botulus from the type-host, Alepisaurus ferox, and to refine the concept of this genus (see Gibson & Bray, 1977). We have also examined the type-specimens of Distomum microporum Monticelli, 1889, present in the collections of the British Museum (Natural History). These specimens were recovered from the type-host (A. ferox) and type-locality (off Madeira) of B. alepidosauri. Although D. microporum has been listed as a species of Hemiurus by some authors (Looss, 1899; Yamaguti, 1971), our examination has convinced us that it is a senior synonym of B. alepidosauri. The morphology of Botulus microporus is described in detail elsewhere (Gibson & Bray, 1977). new species, P. skrjabini, from Alepisaurus aesculapius in Pacific Ocean by A. S. Skrjabin (1958). There with A. the be (which may synonymous ferox), appears to be no significant difference between this genus and Botulus, except for the reported second species, P. alepisauri, was described presence of a globular seminal vesicle in the former. Profundiella was originally erected for a A by Parukhin & Nikolaeva (1967) from Alepisaurus sp. in the Gulf of Mexico (A. ferox appears to be the only species of Alepisaurus recorded in this region); but this species possesses a seminal vesicle which is tubular and coiled. Examination of specimens of Botulus from Alepisaurus ferox 100 D. I. GIBSON & R. A. BRAY from off Miami Beach, Florida, show that they appear to be indistinguishable from B. microporus. seems probable that the apparent globular seminal vesicle of P. skrjabini may in fact be a tightly coiled, tubular form, as a tubular seminal vesicle is the normal condition in primitive hemiuroids. Stunkard (1965) also considered Profundiella as a synonym of Botulus, but it was It listed separately by Yamaguti (1971). & Nikolaeva (1974), we are of the opinion that Mediolecithus pacificus Oshmarin, 1968, belongs to Botulus. One specimen was described by Oshmarin from Lamna cornubica, a piscivorous shark. It is likely that this was an accidental infestation, as Alepisaurus is the normal host of Botulus. In agreement with Parukhin LAMPRITREMA & Hirudinelloides Gaevskaja Yamaguti, 1940 [T(s)] Kovaleva, 1977 Body elongate; slender. Papillae present on forebody. Uroproct absent. Testes in tandem; near middle of hindbody. Most of seminal vesicle thin-walled, but distal portion forms thick-walled, muscular 'pars musculosa'. Thick-walled pars prostatica lies ventral to posterior portion of 'cirrus-sac'. Male duct leads into 'cirrus-sac' some distance from its posterior extremity. 'Cirruslong or short; capable of being extruded some distance atrium Genital deep. Ovary near middle of hindbody. Laurer's canal (?) through genital pore. absent. Seminal receptacle (?) small; enclosed in Mehlis' gland [see below]. Uterus extends back to near posterior limit of vitellarium; mainly coiled inter-caecally in post- and pre-ovarian regions of hindbody. Vitellarium a pair of lateral tubules with short dorsal branches; mainly extra-caecal sac' large; elongate; club-shaped. 'Cirrus' ; passing posteriorly from ovary to about half-way to posterior extremity. Excretory arms appear to unite in forebody (cf. Yamaguti, 1940). Parasitic in stomach (? occasionally on gills) of marine teleosts (Lampris, Brama and Thyrsites). Immature forms recorded from salmonids (stomach, oesophagus or gills). TYPE-SPECIES. Lampritrema miescheri(Zschokke, 1890) [syn. L. nipponicum Yamaguti, 1940 - type by original designation]. We considered separating Lampritrema from Hirudinella and Botulus at the subfamily are no morphological differences which one could definitely consider to be but there level, at the subfamily level. important Notwithstanding the descriptions of Lampritrema atlanticum Delyamure & Serdyukov, 1970, L. hawaiiense Yamaguti, 1970, and Hirudinelloides elongatus Gaevskaja & Kovaleva, 1977, we consider this genus to be monotypic (see Gibson & Bray, 1977). L. savalai Zaidi & Khan, 1977, is clearly a hemiurid. Yamaguti (1940) stated that Laurer's canal was absent in Lampritrema nipponicum and that a small seminal receptacle was present inside Mehlis' gland. We question the absence of Laurer's canal in this species, as it is present in all other primitive hemiuroids, and the small size (up to 105 urn) and location of the seminal receptacle suggests that its presence and nature is questionable: we would expect a uterine seminal receptacle to be present. Neither of these features were commented upon by Margolis (1962) in his redescription of this species. COMMENT. Family ISOPARORCHIIDAE Travassos, 1922 Body large; stout; dorso-ventrally flattened. Ecsoma absent. Body-surface smooth. Oral and ventral suckers small. Pharynx well developed. Oesophagus short. 'Drusenmagen' absent. Gutcaeca sinuous; terminate blindly near posterior extremity. Testes two; symmetrical; pre-ovarian; hindbody. Seminal vesicle small; thin-walled; tubular; winding in forebody. Pars prostatica tubular. Ejaculatory duct within sinus-sac. Sinus-sac weakly developed; composed of diffuse musculature. Hermaphroditic duct short; opens into genital atrium through stout sinusorgan. Genital atrium with pair of concentric folds in its wall; capable of being extruded through in anterior genital pore [see Fig. 2]. Genital pore mid-ventral in forebody. Ovary tubular; well posterior to THE HEMIUROIDEA 101 Laurer's canal present; may be slightly dilated proximally forming small rudimentary seminal receptacle. Uterine seminal receptacle present. Juel's organ and canalicular or blind seminal receptacle absent. Uterus pre-ovarian; mainly coiled in hindbody. Eggs numerous; small; non-filamented. Vitellarium tubular; with dendritic branches arising from about six testes. collecting ducts; post-ovarian. Excretory vesicle Y-shaped; arms come close together dorsal to pharynx, but do not unite. Parasitic in swim-bladder of physostomatous teleosts in freshwater and (Asia Australasia). ISOPARORCHIS Southwell, 1913 [t(w,s)] Leptolecithum Kobayashi, 1915 Defined as family. TYPE-SPECIES. Isoparorchis hypselobagri (Billet, 1898) [syn. by original designation]. Family LECITHASTERIDAE /. trisimilitubis Southwell, 1913 - type Odhner, 1905 Lobatovitelliovariidae Yamaguti, 1965 usually small; normally spindle-shaped, occasionally elongate. Ecsoma absent. Bodysurface smooth. Oral and ventral suckers well developed; ventral sucker normally in anterior Body half of body. Muscular flange or flanges may be present immediately posterior to ventral sucker. Pharynx well developed. Oesophagus usually short. 'Drusenmagen' normally present. Gut-caeca usually terminate blindly, but occasionally unite forming cyclocoel. Presomatic pit and ventrocervical groove absent. Testes two, occasionally one; in tandem; oblique or symmetrical; usually, but not always, pre-ovarian; in hindbody. Seminal vesicle generally thin-walled, occasionally muscular; oval, tubular or constricted into portions; in fore- or hindbody. Pars prostatica usually tubular, occasionally vesicular; may be linked to seminal vesicle by aglandular tube. Ejaculatory duct long, short or absent. Hermaphroditic duct present. Ejaculatory (prostatic) vesicle absent. Sinus-sac usually present; well or poorly developed; occasionally absent. Permanent sinus-organ normally absent, but hermaphroditic duct is often protruded to form temporary sinus-organ. Genital atrium large, small or absent. Ovary usually post-testicular; oval or four- (occasionally three-) lobed. Usually only blind seminal receptacle present (normally large, thick-walled and and Laurer's canal, organ and both uterine or occasionally organ and uterine seminal receptacle present; rarely only Laurer's canal and canalicular seminal receptacle present. Uterus mainly post- to entirely pre-ovarian; main bulk rarely extends into forebody. Eggs numerous; situated dorsal or antero-dorsal to ovary) canalicular seminal receptacles absent; Juel's only Juel's small; rarely filamented. Vitellarium commonly seven-lobed; occasionally six, eight or double these numbers (sometimes branched) lobes often in rosette arrangement; usually immediately post-ovarian, occasionally pre-ovarian or at level of ovary. Excretory vesicle Y-shaped; arms united in forebody or not. Parasitic in gut, especially intestine, of marine teleosts. Key 1. to Lecithasteridae A. B. 2. A. .......... HYSTEROLECITHINAE (p. 104) Uterine seminal receptacle present 2 Uterine seminal receptacle absent Uterus entirely or almost entirely pre-ovarian; hermaphroditic duct appears to be TRIFOLIOVARIINAE (p. 109) continuation of uterus; Laurer's canal may be present 3 Uterus partly post-ovarian; hermaphroditic duct normal Muscular ventro-lateral flange or flanges present immediately posterior to ventral sucker ...... . B. 3. A. QUADRIFOLIOVARIINAE B. 4. A. (p. 108) Muscular ventro-lateral flange or flanges absent immediately posterior to ventral sucker Seminal vesicle in forebody or dorso-lateral to ventral sucker (in one or two species of Lecithaster it may extend into the anterior hindbody, but these can be distinguished from the macradeninines by the well-developed nature of the sinus-sac) . ... 4 5 102 D. I. GIBSON & R. A. BRAY B. Seminal vesicle entirely in hindbody; pars prostatica and/or ejaculatory duct long; sinussac small or poorly developed; usually parasitic in Acanlhurus spp. A. Sinus-sac relatively well developed ; vitellarium post-ovarian LECITHASTERINAE (p. 102) Sinus-sac apparently absent; genital atrium sucker-like; vitellarium pre-ovarian MACRADENININAE (p. 5. B. 105) . PROLECITHINAE LECITHASTERINAE Subfamily Lecithophyllinae Skrjabin & (p. 107) Odhner, 1905 Guschanskaja, 1954 Caeca terminate blindly. Testes two, occasionally one; pre-ovarian. Seminal vesicle in forebody, dorsal to ventral sucker or, occasionally, in anterior hindbody. Pars prostatica short to medium in length. Ejaculatory duct absent or short. Sinus-sac well developed. Permanent sinus-organ absent. Ovary entire or four-lobed. Blind seminal receptacle normally large; usually dorsal to ovary. Uterus reaches to post-ovarian region. Vitellarium seven (rarely six or eight) oval to digitiform lobes in rosette or two linked groups of three and four; immediately post-ovarian; occasionally antero-posteriorly oriented. Excretory arms united in forebody or not. Normally parasitic in intestine or stomach of marine teleosts. Key to Lecithasterinae .............. ...... ......... MONORCHIAPONURUS A. Testis single B. Testes two 2. A. Vitelline lobes tubular B. Vitelline lobes tear-shaped to globular 3. A. Ovary lobed, usually with four lobes; vitelline lobes tear-shaped Ovary oval to globular; vitelline lobes globular 4. A. 1. B. B. QADRIANA ....... . . 2 (inadequately described) . 3 LECITHASTER 4 LECITHOPHYLLUM APONURUS Genital atrium present Genital atrium small or absent LECITHASTER Liihe, 1901 [n(w,s)] Testes two; obliquely symmetrical; usually oval, but occasionally lobed. Seminal vesicle saccular to elongate and sinuous; in forebody, dorsal to ventral sucker or, occasionally, in anterior hindbody. Sinus-sac oval. Genital atrium short. Ovary normally four-lobed. Seminal receptacle large, globular; dorsal to ovary. Vitellarium a radiating mass of seven tear-shaped lobes. Excretory arms apparently not united in forebody. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Lecithaster confusus Odhner, 1905 [by subsequent designation - Odhner, 1905]. COMMENT. Dawes (1947) lists Leptosoma Stafford, 1904 [nee Desmarest, 1825; nee Travassos, 1920; etc.; etc.] as a synonym of Lecithaster; but Stafford's description of Leptosoma obscurum not adequate for a determination, even at the family-level. For this reason, therefore, and because: (1) Leptosoma was not mentioned by Miller (1941), who studied Stafford's material; (2) there are no specimens amongst Stafford's material in the National Museums of Canada, Ottawa; is and (3) lecithasterids recorded ; do not appear we consider to be that this genus is normal parasites ofLophius, from which Leptosoma was unrecognizable. APONURUS Looss, 1907 Brachadena Linton, 1910 (?) Mordvilkoviaster Pigulewsky, 1938 Testes two; tandem to oblique. Seminal vesicle saccular; in forebody or occasionally dorsal to ventral sucker. Hermaphroditic duct usually tubular, occasionally bipartite. Sinus-sac oval to THE HEMIUROIDEA 103 elongate-oval. Genital atrium absent, or occasionally small. Ovary oval or globular. Seminal receptacle small to large; (?) ventral or dorsal to anterior region of ovary. Vitellarium usually seven globular to slightly elongate lobes; in lateral, occasionally antero-posteriorly oriented, groups of three and four. Excretory arms united in forebody. Parasitic in stomach (occasionally intestine) of marine teleosts. TYPE-SPECIES. Aponurus laguncula Looss, 1907 [by monotypy]. COMMENT. The validity of Aponurus as a distinct genus from Lecithophyllum has been a matter of some discussion (see Margolis, 1958). The two genera differ in the presence and absence of a distinct genital atrium. As this is a contractile organ, its use as an important taxonomic criterion should be treated with caution. In this case the character does appear to be of value, as it is a deep and apparently consistent feature in species of Lecithophyllum. It would not be surprising, however, if future workers discovered that, with regard to this feature, the two genera tend to grade into one another: indeed, Lecithophyllum hawaiiense Yamaguti, 1970, may be such a case in point. Yamaguti (1953) used the nature of the hermaphroditic duct to distinguish these two genera species of Lecithophyllum normally possess an hermaphroditic duct which is bipartite, whereas in Aponurus it is supposed to be uniform throughout its length. Yamaguti's (1970) figure of Aponurus acanthuri Manter & Pritchard, 1960, which he placed in Lecithophyllum despite the extremely small size of the genital atrium, and Overstreet's (1973) figure of A. pyriformis : (Linton, 1910) indicate that these species have bipartite hermaphroditic ducts. With regard to the status of Brachadena Linton, 1910, Yamaguti (1953, 1958, 1971) considered this genus a synonym of Lecithophyllum, whereas Margolis (1958) believed it to be distinct on & Kuntz the basis of a central union of the vitelline lobes. Contrary to the work of Fischthal (1964c), which showed that a small genital atrium is present in the type-species, B. pyriformis Linton, 1910, Overstreet (1973) demonstrated that there is no distinct genital atrium present: Yamaguti's (1971) figure of the paratype also indicated that there is no genital atrium present. Overstreet's work showed that the type-species has an antero-posteriorly oriented vitellarium, the three- and four-lobed groups of which being united by a short duct. In view of the questionable validity of Aponurus itself, we feel that any variations in the nature and orientation of the vitellarium and in the hermaphroditic duct of Brachadena pyriformis, as compared with other species of Aponurus, should be regarded as being of only specific value. Aponurus priacanthi Yamaguti, 1970, does not appear to be a lecithasterine. A uterine seminal and possibly a Juel's organ are shown in Yamaguti's figure of this species. We have tentatively included Mordvilkoviaster Pigulewsky, 1938, as a synonym of Aponurus, as both Looss (1908) and Pogoreltseva (1952) have described Lecithaster galeatus Looss, 1907, the type-species, as having a round ovary. Skrjabin & Guschanskaja (1954) and Yamaguti (1971) consider Mordvilkoviaster to be a synonym of Dichadena Linton, 1910; but we believe that the sinus-sac is too well developed, the seminal vesicle too anterior and the pars prostatica too short for it to be considered a macradeninine. receptacle LECITHOPHYLLUM Odhner, 1905 [t(w,s)] Testes two; obliquely tandem to symmetrical. Seminal vesicle saccular; in forebody or dorsal to ventral sucker. Hermaphroditic duct apparently bipartite. Sinus-sac elongate. Genital atrium present; generally deep. Ovary oval or globular. Seminal receptacle large; dorsal to ovary. Vitellarium seven globular lobes, in lateral groups of three and four. Excretory arms united in forebody. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Lecithophyllum botryophoron (Olsson, 1868) [by original designation]. COMMENT. Brinkmann figured a sinus-organ. (1977), in his detailed redescription of the type-species, described and other species in this family, this structure is temporary: it is not As with A temporary sinus-organ, present in our material of this species (fixed in glacial acetic acid). however, can be extruded in artificially relaxed, slowly fixed or frozen material. 104 D. (?) I. GIBSON & BRAY R. A. MONORCH1APONURUS Fischthal & Nasir, 1974 Testis single. Seminal vesicle saccular; in forebody. Sinus-sac elongate. Hermaphroditic duct tubular. Genital atrium absent. Ovary oval. Seminal receptacle pre-ovarian; postero-dextral to testis. Vitellarium seven globular lobes. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Monorchiaponurus hemirhamphi Fischthal COMMENT. This genus amongst is known from & only one specimen. Nasir, 1974 [by original designation]. As the absence of one testis is not a possible that this specimen is merely an abnormal example of Aponurus. More specimens, as in the case of Monorchimacradena Nahhas Cable, 1964, are required before this genus can be fully accepted. In listing this genus independently of Aponurus, we are assuming that the seminal receptacle, which is rather far anterior rare feature bi-testicular digeneans, it is & for a lecithasterid, has not been confused with the second testis. (?) QADRIANA Bilqees, 1971 [Inadequately described.] Testes two; tandem; postero-lateral to ventral sucker. Seminal vesicle saccular; in forebody. Ovary oval. 'Seminal receptacle not obvious.' Vitellarium 'composed of several tubes'. Uterus extra-caecal in hindbody. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Qadriana fusiformis Bilqees, 1971 [by monotypy]. Subfamily HYSTEROLECITHINAE Yamaguti, 1958 Body small; elongate to spindle-shaped. Ventral sucker in middle or anterior half of body. Gut-caeca end blindly near posterior extremity. Testes two; oval; symmetrical to obliquely tandem; pre-ovarian; in anterior half of hindbody. Seminal vesicle usually tubular, occasionally elongate saccular; in forebody. Pars prostatica usually tubular, occasionally vesicular; short. Sinus-sac present; often weakly developed; occasionally of open-type. Permanent sinus-organ absent; temporary sinus-organ may form. Hermaphroditic duct present within sinus-sac. Genital atrium small or absent. Ovary oval; in anterior or posterior half of hindbody. Laurer's canal and blind or canalicular seminal receptacle absent. Juel's organ and uterine seminal receptacle present [see below]. Uterus almost entirely in hindbody; mainly pre- to mainly post-ovarian. Eggs with or without filaments. Vitellarium seven (occasionally eight) oval to digitiform lobes; post-ovarian. Excretory arms united in forebody or not. Parasitic mainly in intestine or stomach of marine teleosts (usually perciform genera, especially acanthurids COMMENT. There appears to have been and pomacentrids). some confusion between the genera of this subfamily and We certain other lecithasterid genera. have, therefore, taken our definitions only from species in which the presence of a uterine seminal receptacle or the absence of a blind or canalicular seminal receptacle has been indicated. Although Juel's organ has not been reported previously in this group, we found it to be well developed in a paratype specimen of Hysterolecitha elongata Manter, 1931, from the H. W. Manter Collection, which Dr M. H. Pritchard kindly allowed us to section. of Hysterolecithoides epinepheli referred to a large seminal receptacle in addition to a uterine seminal receptacle, and in his (1942) description of Hysterolecitha nahaensis he referred to a small seminal receptacle in addition to a uterine seminal receptacle. Unless a similar variation to that present in the Derogeninae occurs in this subfamily, it is probable that the organ described by Yamaguti as a seminal receptacle is Juel's organ. Yamaguti (1934) Key 1. to Hysterolecithinae A. B. 2. in his description A. B. ............ Eggs filamented Eggs without filaments Excretory arms united in forebody; uterus mainly pre-ovarian Excretory arms not united in forebody; uterus mainly post-ovarian . THULINIA 2 HYSTEROLECITHA HYSTEROLECITHOIDES . THE HEMIUROIDEA 105 COMMENT. In order to identify a genus from this subfamily, it is essential that eggs are teased from the body and that the anterior regions of the excretory system are examined. The latter normally necessitates sectioning. It is clear, in species where the excretory system has not been fully described, that there has been some confusion between Hysterolecitha and Hysterolecithoides. For example, although the excretory system was not fully described, Yamaguti (1971) placed Hysterolecithoides pseudorosea Bravo-Hollis, 1956, in the genus Hysterolecitha, despite the position of the ovary and the distribution of the uterus which suggested that Bravo-Hollis (1956) was correct. HYSTEROLECITHA Union, 1910 [n(w,s)] Ventral sucker usually in anterior half of body occasionally near middle. Seminal vesicle normally tubular; occasionally elongate saccular. Pars prostatica tubular; occasionally vesicular. Sinus-sac present; often weakly developed; may be of 'open'-type. Ovary normally in posterior half of ; hindbody; normally separated from testes by loops of uterus. Uterus usually mainly pre-ovarian; (?) occasionally mainly post-ovarian. Eggs without filaments. Excretory arms united in forebody. TYPE-SPECIES. Hysterolecitha rosea Linton, 1910 [by original designation]. HYSTEROLECITHOIDES Yamaguti, 1934 Ventral sucker in middle of body. Seminal vesicle tubular. Pars prostatica tubular or vesicular. Sinus-sac oval. Ovary close to testes. Uterus mainly post-ovarian. Eggs without filaments. Excretory arms not united in forebody. TYPE-SPECIES. Hysterolecithoides epinepheli Yamaguti, 1934 [by original designation]. THULINIA gen. nov. elongate. Ventral sucker in anterior half of body. Gut-caeca end blindly near posterior extremity. Testes two; oval; obliquely tandem; separated from ventral sucker and ovary by loops of uterus. Seminal vesicle tubular; in forebody; may reach dorsally to ventral sucker. Pars prostatica tubular; short. Sinus-sac present; well developed. Permanent sinus-organ absent; Body temporary sinus-organ may form. Hermaphroditic duct present within sinus-sac. Genital atrium small. Genital pore mid-ventral near middle of forebody. Ovary oval in posterior half of hindbody. Laurer's canal presumed absent. Canalicular or blind seminal receptacle absent. Juel's organ and uterine seminal receptacle presumed present. Uterus almost entirely in hindbody; coiled in pre- and post-ovarian fields. Eggs filamented (one filament at each end). Vitellarium seven (or eight) digitiform lobes; post-ovarian. Excretory vesicle Y-shaped; excretory arms united in forebody. Parasitic in intestine of marine teleosts. ; TYPE-SPECIES. Thulinia tinkeri (Manter & Pritchard, 1960) n. comb. COMMENT. We have erected this genus because of the presence of filaments on the eggs, a feature which we believe to be a good generic criterion. It is named after Mr Jan Thulin, University of Gothenburg, who has helped us with several aspects of our work. Subfamily MACRADENININAE Skrjabin & Guschanskaja, 1954 Gut-caeca usually end blindly, but cyclocoel sometimes present. Testes two, occasionally one; oval; usually pre-ovarian, but may be at level of ovary or post-ovarian. Seminal vesicle in hindbody; saccular, tri-partite or tubular. Pars prostatica tubular; long. Ejaculatory duct usually short or absent. Sinus-sac present; small; may be poorly developed. Permanent absent. sinus-organ Ovary four-lobed or oval. Blind seminal receptacle present. Uterus reaches to post-ovarian region. Vitellarium immediately anterior, at level of or immediately posterior to ovary; variable, commonly six- to eight-lobed, but may be seven branched lobes, or twelve or long, but may be 106 D. I. GIBSON & R. A. BRAY fourteen lobes, and group of lobes may be antero-posteriorly oriented. Excretory arms united in forebody or not. Parasitic in intestine or stomach of marine teleosts (normally Acanthurus spp.). Key 1. to Macradenininae A. B. Vitellarium consisting of 6 to 8 (usually 7) tear-shaped or slightly branched lobes; seminal vesicle saccular (? or tubular) Vitellarium consisting of 12 or more lobes (occasionally 7 basic lobes divided into about .............. 40 secondary lobes) which may be tubular or globular; seminal tri-partite 2. 3. 4. A. 2 vesicle tubular or 5 PSEUDODICHADENA B. Ovary 4-lobed Ovary unlobed A. Testis single B. Testes 2 4 Testes at level of ovary; vitellarium antero-lateral to ovary; seminal vesicle (?) saccular or DICHADENA (?) tubular Testes pre-ovarian; vitellarium post-ovarian; seminal vesicle saccular (? with constriction) A. B. . . . . 3 MONORCHIMACRADENA ..... NEODICHADENA 5. A. B. 6. A. B. Seminal vesicle tubular; vitelline lobes elongate, in single group 6 Seminal vesicle tri-partite; vitelline lobes globular, in 2 groups, 7 anterior and 7 posterior to ovary ACANTHURITREMA Testes post-ovarian; vitellarium 12 claviform lobes, ventral to ovary MACRADENINA Testes pre-ovarian; vitellarium essentially 7 lobes, but divided into about 40 secondary MACRADENA lobes, between ovary and seminal vesicle . ...... COMMENT. We have retained all of the genera in this subfamily because of conflicting accounts of their morphology and in view of Yamaguti's (1971) examination of many of the holotypes; but it is likely that some of these forms will prove to be synonymous. Several of the genera require the study of fresh material before their validity can be confirmed, and a redescription of Dichadena acuta Linton, 1910, especially is needed. This subfamily appears to be almost entirely restricted to fishes of the genus Acanthurus from the central American region and Hawaii. MACRADENINA Manter, 1947 Cyclocoel not reported. Testes tandem; post-ovarian. Seminal vesicle tubular; loosely coiled at of ovary. Pars prostatica long. Ejaculatory duct (?) absent. Sinus-sac sub-cylindrical; may be incomplete posteriorly; appears to be protrusible. Ovary four-lobed; well forward in hindbody. Seminal receptacle globular; large; post-ovarian. Vitellarium twelve claviform, unbranched level tubules; ventral to ovary. Excretory arms (?). TYPE-SPECIES. Macradenina acanthuri Manter, 1947 [by original designation]. ACANTHURITREMA Yamaguti, 1970 Cyclocoel not reported. Testes tandem to oblique; pre-ovarian. Seminal vesicle tri-partite; posterior part large and spherical, middle part elongate elliptical, anterior part pyriform; connected to pars prostatica by aglandular duct; in anterior hindbody. Pars prostatica short. Ejaculatory duct absent. Sinus-sac thin, membranous; indistinct. Ovary four-lobed. Seminal receptacle large; antero-dorsal to ovary. Vitellarium fourteen globular lobes; seven anterior and seven posterior to ovary. Excretory arms not united in forebody. TYPE-SPECIES. Acanthuritrema multivitellosum Yamaguti, 1970 [by original designation]. DICHADENA Linton, 1910 Cyclocoel (?) not reported (except in key by Yamaguti, 1971). Testes tandem; dorsal to ovary. Seminal vesicle sac-like (tubular according to Yamaguti, 1971); immediately pre-testicular. Pars THE HEMIUROIDEA 107 prostatica long; dilate posteriorly. Ejaculatory duct similar in length to pars prostatica. Sinus-sac oval. Ovary oval [four-lobed according to Manter, 1947: specimens with four-lobed ovary & described by Siddiqi Cable, 1960, as D. acuta, now placed in Pseudodichadena]. Seminal receptacle between posterior margin of ovary and posterior testis. Vitellarium six or seven rounded to tear-shaped lobes; antero-lateral to ovary. Excretory arms (?). TYPE-SPECIES. Dichadena acuta Linton, 1910 [by original designation]. MACRADENA Linton, 1910 Cyclocoel not reported. Testes tandem; pre-ovarian. Seminal vesicle tubular; coiled in anterior hindbody. Pars prostatica long. Ejaculatory duct about one quarter length of pars prostatica. Sinus-sac weakly developed and small. Ovary four ovoid lobes. Seminal receptacle large; oval; immediately posterior to ovary. Vitellarium originates between ovary and seminal receptacle; consists of seven main radial lobes which are finely divided to form about forty fairly short, tubular lobes. Excretory arms united in forebody. TYPE-SPECIES. Macradena perfecta Linton, 1910 [by original designation]. MONORCHIMACRADENA Nahhas & Cable, 1964 Cyclocoel not reported. Testis single; immediately pre-ovarian. Seminal vesicle sac-like; immediately pre-testicular. Pars prostatica and ejaculatory duct about equal in length. Sinus-sac spherical to pyriform; small. Ovary oval. Seminal receptacle as large or larger than ovary; dorsal to ovary. Vitellarium seven digitiform or slightly branched lobes; united centrally; post-testicular. Excretory arms united in forebody. TYPE-SPECIES. Manor chimacradena acanthuri Nahhas NEO DICHADENA & Cable, 1964 [by original designation]. Yamaguti, 1971 Cyclocoel not reported. Testes oblique; immediately pre-ovarian. Seminal vesicle sac-like (may have constriction). Pars prostatica long. Ejaculatory duct about half length of pars prostatica. Sinus-sac small; spherical. Ovary oval. Seminal receptacle large; lateral to ovary. Vitellarium about eight tear-shaped lobes; post-ovarian. Excretory arms united in forebody. TYPE-SPECIES. Neodichadena acanthuri (Siddiqi & Cable, 1960) [by original designation]. PSEUDODICHADENA Yamaguti, 1971 Cyclocoel present. Testes small tandem at level of ovary. Seminal vesicle elliptical dorsal at of gonads. Pars prostatica long. Ejaculatory duct short. Sinus-sac oval. Ovary four-lobed. Seminal receptacle post-ovarian. Vitellarium seven tear-shaped lobes; antero-lateral to ovary. Excretory arms united in forebody. ; ; ; level TYPE-SPECIES. Pseudodichadena lobata Yamaguti, 1971 [syn. Dichadena acuta of Siddiqi 1960, nee Linton, 1910] [by original designation]. Subfamily Folliovitellotrematinae Gupta & PROLECITHINAE Sharma, 1972 & Cable, Yamaguti, 1971 (sic) Body spindle-shaped. Ventral sucker large, prominent. Cyclocoel present. Testes two; diagonal to symmetrical; at level of or slightly posterior to ventral sucker. Seminal vesicle saccular; in forebody. Pars prostatica short; vesicular. Sinus-sac and permanent sinus-organ absent. Large, spherical genital atrium present with muscular walls forming sucker-like structure (it is possible that this structure is an hermaphroditic duct surrounded by the remains of a sinus-sac). Ovary three- to four-lobed; near posterior extremity; overlying cyclocoel. Blind seminal receptacle D. 108 I. GIBSON & R. A. BRAY to gonads. Vitellarium posterior to ovary; at posterior extremity of body. Uterus mainly anterior seven rounded lobes; immediately pre-ovarian; close to testes. Excretory arms not united in forebody. Parasitic in intestine of marine teleosts (Belonidae). PROLECITHA Manter, 1961 Lobatovitelliovarium Yamaguti, 1965 Follicovitellosum Gupta Sharma, 1972 & As subfamily. TYPE-SPECIES. Prolecitha obesa Manter, 1961 [by original designation]. Subfamily QUADRIFOLIOVARINAE Yamaguti, 1970 Body elongate to spindle-shaped. Muscular ventro-lateral flange or flanges present immediately posterior to ventral sucker. Caeca usually terminate blindly, but cyclocoel may be present. Testes two; pre-ovarian. Seminal vesicle in hindbody; saccular, constricted into portions or tubular. Pars prostatica usually short; tubular; in hindbody. Ejaculatory duct long; may be lined with cuticular villi. Sinus-sac oval. Permanent sinus-organ absent. Genital atrium short or apparently absent. Ovary oval or four-lobed. Blind seminal receptacle normally large; anterior or antero-dorsal to ovary. Uterus reaches to post-ovarian region. Vitellarium seven post-ovarian, claviform or oval lobes, or two groups of six to seven digitiform lobes, one pre-ovarian and one post-ovarian. Excretory arms united in forebody. Parasitic in stomach or pyloric caeca of acanthurid marine teleosts. COMMENT. This subfamily is morphologically similar to the Macradenininae, differing fundamentally only in the presence of muscular flanges just posterior to the ventral sucker and in the length of the pars prostatica. It is worth noting that all of the macradeninine and quadrifoliovariine genera are parasitic in acanthurid teleosts. Key 1. to Quadrifoliovariinae A. Muscular ventro-lateral flange present on one side of body only; cyclocoel present B. A. Muscular ventro-lateral flanges symmetrical; cyclocoel absent Ovary 4-lobed; vitelline lobes in 2 antero-posteriorly oriented groups B. Ovary oval; ..... UNILACINIA 2. vitelline lobes in one group ....... QUADRIFOLIOVARIUMYamaguti, 2 Q UA DRIFOLIO VA RWM BILAC1N1A 1965 Pair of muscular ventro-lateral flanges immediately posterior to ventral sucker. Cyclocoel not reported. Testes tandem. Seminal vesicle a wide, convoluted tube; narrowing anteriorly. Pars prostatica short. Ejaculatory duct two to three times length of pars prostatica. Hermaphroditic may be everted to form temporary sinus-organ. Sinus-sac thin-walled; elliptical Ovary four-lobed. Vitellarium in two antero-posteriorly oriented rosette-like groups; one pre- and one post-ovarian; united by collecting duct; each group has six or seven digitiform lobes. Parasitic in stomach and pyloric caeca of marine teleosts (Naso). duct convoluted; to oval. TYPE-SPECIES. Quadrifoliovarium pritchardae Yamaguti, 1965 [by original designation]. BILAC1N1A Manter, 1969 Holacanthitrema Yamaguti, 1970 Pair of bilobed, muscular ventro-lateral flanges; symmetrical; immediately posterior to ventral sucker. Cyclocoel not reported. Testes tandem to oblique. Seminal vesicle convoluted, wide and THE HEMIUROIDEA 109 tubular or divided into four to five portions. Pars prostatica sigmoid. Ejaculatory duct one quarter to nearly equal length of pars prostatica. Hermaphroditic duct wide; straight. Sinus-sac oval; thin-walled. Ovary oval. Vitellarium seven rounded to claviform lobes; immediately post-ovarian. Parasitic in stomach and pyloric caeca of marine teleosts (Naso and Holacanthus}. TYPE-SPECIES. Bilacinia australis Manter, 1969 [by original designation]. UNIL ACINIA Manter, 1969 Bilobed muscular flange lateral to ventral sucker, on one side only. Cyclocoel present. Testes oblique. Seminal vesicle saccular; antero-dorsal to anterior testis. Ejaculatory duct twice length of pars prostatica. Hermaphroditic duct wide. Sinus-sac broadly ovoid. Ovary oval. Vitellarium seven short, digitiform lobes; postero-ventral to ovary. Parasitic in stomach of marine teleosts (Naso). TYPE-SPECIES. Unilacinia asymmetrica Manter, 1969 [by original designation]. Subfamily TRIFOLIOVARIINAE Yamaguti, 1958 Body cylindrical; long and thin, fusiform or elongate oval. Ventral sucker present well inside anterior half of body. Gut-caeca terminate blindly; often wide. Testes two; pre-ovarian in anterior hindbody; separated from ovary by many loops of uterus. Seminal vesicle in forebody, at level of ventral sucker or in hindbody; tubular, moniliform or elongate oval. Pars prostatica short; tubular or vesicular. Ejaculatory duct short; enters hermaphroditic duct, which is continuation of uterus, laterally. Sinus-sac present surrounding hermaphroditic duct; weak and membranous; tubular or oval. Permanent sinus-organ absent. Genital atrium absent or small. Female reproductive complex close to posterior extremity. Ovary four-lobed. Laurer's canal present or absent. Seminal receptacle large; blind or canalicular; dorsal or antero-dorsal to ovary. Uterine seminal receptacle and Juel's organ absent. Uterus entirely or almost entirely pre-ovarian; coils confined to hindbody. Eggs without filaments. Vitellarium seven or eight claviform or digitiform lobes, which may be bilobed or irregularly branched distally; at level of ovary or immediately post-ovarian. Excretory arms united marine teleosts. Key 1. in forebody. Parasitic in intestine of to Trifoliovariinae A. B. Body long and thin; seminal vesicle in hindbody or dorsal (to antero-dorsal) to ventral sucker, elongate oval (to tubular and sinuous); vitelline lobes claviform, unbranched, TRIP OLIO in rosette arrangement ; Laurer's canal present Body elongate oval to fusiform; seminal vesicle in forebody or antero-dorsal to ventral .... VARIUM .............. ......... sucker, tubular, moniliform or elongate oval; Laurer's canal absent [or at least not reported] 2. Seminal vesicle elongate oval vitellarium a rosette of 12 to 16 lobes (possible B. 3 Seminal vesicle tubular or moniliform Uterus mainly intercaecal; vitellarium 2 groups of 4 unbranched posteriorly oriented ASSITREMA tubular lobes; seminal vesicle moniliform, antero-dorsal to ventral sucker Uterus reaches extracaecally; vitellarium a rosette arrangement of 7 short tubular distally CLADOLECITHOTREMA branched lobes; seminal vesicle tubular, in forebody ; PSEUDOLECITHASTER lobes); pars prostatica vesicular 3. 2 ca. 7 bilobed A. A. . B. . . TRIFOLIO VA RIUM Yamaguti , 1 940 [T(w) ] Body long and thin. Oral sucker funnel-shaped. Testes tandem to oblique; widely separated. Seminal vesicle elongate oval (or tubular and sinuous); in hindbody or dorsal to ventral sucker (or antero-dorsal to ventral sucker) connected to pars prostatica by short, aglandular duct. Pars prostatica tubular. Sinus-sac tubular. Laurer's canal present, uniting canalicular seminal receptacle with dorsal surface. Vitellarium seven claviform lobes at level of ovary. ; 110 D. I. GIBSON & R. A. BRAY TYPE-SPECIES. Trifoliovarium acanthocepolae Yamaguti, 1940 [by original designation]. COMMENT. Yamaguti (1940) originally described the ovary as being three-lobed; hence the generic name, but later (1971) corrected this observation to four-lobed. Having examined the type-material of T. acanthocepolae, we can confirm this emendation. The information given above in parentheses is taken from the descriptions of T. triacanthi Bilqees, 1973, and T. triacanthusi Gupta & Ahmad, 1976. These species, which are probably synonymous, were described from Triacanthus spp. off the Indian sub-continent. ASSITREMA Body Parukhin, 1976 small; oval to elongate oval. Gut-caeca wide. Testes symmetrical; separated by coils of Seminal vesicle short, moniliform; winding antero-dorsally to ventral sucker. Pars uterus. prostatica tubular (but wider in middle according to figure). Sinus-sac small; oval. Laurer's canal (?). Seminal receptacle (? blind or canalicular) present. Uterus almost entirely pre-ovarian; mainly inter-caecal. Eggs small. Vitellarium two symmetrical groups of four postero-laterally oriented, digitiform lobes; centre of each group immediately post-ovarian. Excretory arms(?). TYPE-SPECIES. Assitrema eichleri Parukhin, 1976 [by original designation]. COMMENT. Parukhin's (1976c) figure indicates that the hermaphroditic duct is a continuation of the ejaculatory duct. In the other three genera of this subfamily the hermaphroditic duct is a continuation of the metraterm. This may be just a matter of interpretation, for there is no evidence that Parukhin sectioned either of his two specimens. There is a possibility, if the two specimens of Assitrema were young, that some of the differences between this genus and Cladolecithotrema are the result of age. This question cannot be resolved until further material of Assitrema is studied. CLADOLECITHOTREMA Ichihara, 1970 [T(w,s)] Body elongate oval. Gut-caeca wide. Testes oblique; widely separated. Seminal vesicle tubular; convoluted in forebody. Pars prostatica tubular. Sinus-sac small; oval. Laurer's canal absent. Blind seminal receptacle present. Uterine field reaches extra-caecally. Vitellarium a rosette arrangement of seven digitiform, distally branched lobes; centre immediately post-ovarian. TYPE-SPECIES. Cladolecithotrema callionymi Ichihara, 1970 [by original designation]. & Sharma's (1975) proposed synonymy of CladoleCOMMENT. We do not agree with Gupta cithotrema and Trifoliovarium. We consider that the shape and position of the seminal vesicle, the shape of the Vitellarium and the absence or presence of Laurer's canal are sufficient criteria to distinguish these taxa. PSEUDOLEC1TH ASTER Body Campbell & Munroe, 1977 fusiform. Testes symmetrical; separated by coils of uterus. Seminal vesicle elongate oval; connected to pars prostatica by short aglandular duct. Pars prostatica vesicular. in forebody; 'several irregular lobes' (four visible in figure). Laurer's Vitellarium a rosette of twelve to sixteen lobes (figure suggests at level of ovary. Sinus-sac small; elongate oval. canal (?). Seminal receptacle ca. seven bilobed lobes) ; Ovary (?). TYPE-SPECIES. Pseudolecithaster antimorae Campbell Family & Munroe, 1977 PTYCHOGONIMIDAE [by original designation]. Dollfus, 1937 Body medium sized; oval. Ecsoma absent. Body-surface smooth, without spines or plications. Oral and ventral suckers well developed; oral sucker larger than ventral sucker; latter situated in anterior half of body. Pharynx well developed. Oesophagus short. 'Driisenmagen' absent. Gutcaeca form uroproct. Testes two; post-ovarian; tandem; in middle of hindbody. Seminal vesicle dilate, tubular; thin- walled; extending posteriorly into anterior hindbody. Pars prostatica THE HEMIUROIDEA 1 1 1 Ejaculatory and hermaphroditic duct short. Permanent sinus-organ a small cone. Sinus-sac absent. Genital atrium contains three distinct concentric folds in its wall which surround sinus-organ. Genital pore mid-ventral in forebody. Ovary oval; pre-testicular in hindbody. tubular. Mehlis' gland pre-ovarian. Laurer's canal and uterine seminal receptacle present. Juel's organ and canalicular or blind seminal receptacle absent. Uterine field extends between level posterior to testes and ventral sucker. Eggs numerous; without filaments. Vitellarium follicular; occurs in lateral fields extending throughout most of hindbody. Excretory vesicle Y-shaped; arms unite twice in forebody. Parasitic in stomach of elasmobranchs (normally carchariniform sharks). PTYCHOGONIMUS Liihe, 1900 [t(w,s)] Defined as family. TYPE-SPECIES. Ptychogonimus megastoma (Rudolphi, 1819) [by monotypy]. COMMENT. The above ' definition does not take into account the description of 'Ptychogonimus megastoma' given by Vigueras (1956), which differs from other descriptions markedly and requires confirmation. We have examined one type-specimen (whole-mount) of Ptychogonimus fontanus Lyster, 1939, and consider that, although it is not in good condition, this specimen appears to be an azygiid, bearing a strong resemblance to contracted forms of Azygia longa (Leidy, 1851). Family SCLERODISTOMIDAE Odhner, 1927 Prosogonotrematidae Vigueras, 1940 Bhaleraoiidae Srivastava, 1948 Mabiaramidae Teixeira de Freitas Kohn, 1967 & Body usually large; stout or elongate. Ecsoma absent. Body-surface smooth, but may be rugate. Oral and ventral suckers well developed ventral sucker just posterior to middle, in middle or in anterior half of body. Pharynx well developed. Oesophagus short. 'Driisenmagen' present or absent. Gut-caeca terminate blindly close to posterior extremity. Testes two; symmetrical, oblique or in tandem; pre-ovarian; in forebody, dorsal to ventral sucker or in anterior hindbody. Seminal vesicle tubular; convoluted or winding in forebody. Pars prostatica tubular, occasionally with wide lumen; long; convoluted or not; external gland-cells may be delimited. Ejaculatory duct present; unites with metraterm within sinus-organ forming short hermaphroditic duct. ; Permanent sinus-organ usually well developed; conical to cylindrical. Sinus-sac well developed, weakly developed or apparently absent. Genital atrium well developed; often almost entirely filled by sinus-organ. Genital pore mid-ventral in forebody. Ovary globular to oval; well posterior to and usually separated from testes by loops of uterus; in posterior forebody, dorsal to ventral sucker or anterior to mid-hindbody. Mehlis' gland usually posterior or postero-lateral, occasionally antero-lateral, to ovary. Laurer's canal present; opens dorsally or into rudimentary Juel's organ. Rudimentary seminal receptacle present or absent. Canalicular or blind seminal receptacle absent. Uterine seminal receptacle present. Uterus mainly in either fore- or hindbody; mainly pre- or post-ovarian. Eggs small; numerous; non-filamented. Vitellarium four to seven convoluted, tubular branches, which may subdivide; either mainly pre- or post-ovarian; either mainly in fore- or hindbody. Excretory vesicle Y-shaped; stem relatively long; arms united in forebody. Manter's organ (accessory excretory vesicle) present; single or double; dorsal to stem of excretory vesicle. Parasitic in gut (mainly stomach) (?), occasionally in body-cavity, of marine teleosts. COMMENT. Parukhin (1976b) erected a new subfamily, the Pseudosclerodistomoidinae, within this family for Pseudosclerodistomoides kurotchkini, a new genus and species from the gall-bladder of Lethrinus miniatus in the Indian Ocean. Several features of this species, such as the position of the testes and the genital pore and the nature of the seminal receptacle, suggest that it is not a hemiuroid. 112 Key 1. D. R. A. BRAY to Sclerodistomidae ......... A. SCLERODISTOMINAE (p. 112) Manter's organ double; testes in anterior hindbody Manter's organ single; testes in forebody 2 Ovary in forebody or at level of ventral sucker; uterus and vitellarium mainly pre-ovarian B. Ovary A. B. 2. GIBSON & I. . . PROSOGONOTREMATINAE (p. in hindbody; uterus and vitellarium mainly post-ovarian Subfamily SCLERODISTOMINAE . PROSORCHIINAE (p. 112) 112) Odhner, 1927 Body stout. Ventral sucker near middle of body. 'Driisenmagen' present. Testes symmetrical to oblique; in anterior hindbody. Pars prostatica long and convoluted. Sinus-sac distinctly present; musculature diffuse; surrounding base of genital atrium. Sinus-organ a stout cone. Ovary near or just anterior to middle of hindbody. Laurer's canal opens dorsally. Rudimentary seminal receptacle present. Uterus almost entirely in hindbody; mainly posterior to gonads, reaching near to posterior extremity. Vitellarium composed of convoluted, tightly helical, unbranched, filamentous tubules; commonly arranged with three on one side of body, four on other; present laterally in post-testicular region of hindbody. Manter's organ (accessory excretory vesicle) double; symmetrical. Parasitic in stomach and (?) body-cavity of marine teleosts. SCLEROD1STOMUM Looss, Mabiarama Teixeira de Freitas & 1912 [t(w,s) ; n(w)] Kohn, 1967 Defined as subfamily. TYPE-SPECIES. Sclerodistomum italicum (Stossich, 1893) [by monotypy]. Subfamily PROSOGONOTREMATINAE Vigueras, 1940 Body stout. Ventral sucker in middle or just posterior to middle of body. 'Driisenmagen' absent. Testes symmetrical; in forebody. Pars prostatica long and sinuous or convoluted. Sinus-sac well developed, but composed of diffuse musculature. Sinus-organ conical to cylindrical. Ovary in forebody or at level of ventral sucker. Laurer's canal short; opens into large rudimentary Juel's organ; dilated proximally forming small rudimentary seminal receptacle. Rudimentary Juel's organ post-ovarian [distinct in sections] Uterus mainly pre-ovarian does not extend into hindbody. Vitellarium about three (two to four) convoluted, tubular branches on each side of body, which may subsequently divide; mainly pre-ovarian in forebody. Manter's organ (accessory excretory vesicle) single; median. Parasitic mainly in stomach of marine teleosts. . PROSOGONOTREMA ; Vigueras, 1940 [t(w,s)] (?) Bhaleraoia Srivastava, 1948 Defined as subfamily. TYPE-SPECIES. Prosogonotrema bilabiatum Vigueras, 1940 [by monotypy]. COMMENT. Nasir (1973) considers this genus to be monotypic, synonymizing seven other species with P. bilabiatum. We have included Bhaleraoia Srivastava, 1948, as a questionable synonym of this genus, because, although similar in gross morphology, it is poorly described and purported to possess a uroproct. Subfamily Body elongate oval PROSORCHIINAE Yamaguti, 1934 to elongate. Ventral sucker normally within anterior half of body, but 'Driisenmagen' absent. Testes tandem to almost symmetrical; in forebody occasionally in middle. or dorsal to ventral sucker. Pars prostatica broad; usually straight or arcuate; lumen wide; THE HEMIUROIDEA 113 external gland-cells delimited. Sinus-sac apparently absent or (?) weakly developed. Sinus-organ conical to cylindrical. Ovary in hindbody. Laurer's canal long and opening into rudimentary Juel's organ or short and opening to exterior on dorsal surface; may or may not be dilate proxi- mally forming rudimentary seminal receptacle. Uterus mainly post-ovarian in hindbody. Vitellarium two to four branching or seven convoluted and filamentous tubules; mainly postovarian in hindbody; reaching near to posterior extremity. Manter's organ (accessory excretory vesicle) single; median. Key 1. to Prosorchiinae A. B. Laurer's canal long, opening into rudimentary Juel's organ, dilated proximally forming PROSORCHIS rudimentary seminal receptacle Laurer's canal short, opening' dorsally to exterior; rudimentary seminal receptacle absent PROSORCHIOPSIS COMMENT. These two closely related genera essentially appear to differ only in the nature of As few authors appear to have sectioned their material, many of the descriptions in the literature must be used with some degree of caution. Nevertheless, both from the literature Laurer's canal. and from our own sectioned material of Prosorchiopsis, it is evident that two distinct forms of Laurer's canal appear to be present. PROSORCHIS Yamaguti, 1934 Laurer's canal long; opens distally into well-developed rudimentary Juel's organ ('terminal vesicle'); dilate proximally forming rudimentary seminal receptacle. TYPE-SPECIES. Prosorchis psenopsis Yamaguti, 1934 [by original designation]. COMMENT. The presence of a 'terminal vesicle' at the distal extremity of Laurer's canal has been reported in a number of descriptions of species from this genus. Considering the nature of these descriptions, especially that of Yamaguti (1934), and the structure of the related Prosogonotrema, we have interpreted this 'terminal vesicle' as being a rudimentary Juel's organ. PROSORCHIOPSIS Dollfus, 1947 Laurer's canal short; opening dorsally to exterior; distal region possess glandular wall; rudimentary seminal receptacle absent. [t(w,s)] may be slightly dilate and TYPE-SPECIES. Prosorchiopsis legendrei Dollfus, 1947 [by original designation]. material, part of the distal region of Laurer's canal was slightly dilate and a Bray, 1977). It is possible that this represents diffuse, glandular wall (see Gibson possessed an early stage in the development of a rudimentary Juel's organ. It should be pointed out that a uterine seminal receptacle was not present in our sectioned COMMENT. In sectioned & and its presence or absence could not be ascertained either from the literature or from whole-mounts. Considering that there is no alternative seminal storage apparatus and that it is present in Prosorchis, we can only assume that it is normally present in Prosorchiopsis. material, Addendum to Sclerodistomidae possible that Eurycoelum Brock, 1886, and Distoma gigas Nardo, 1827, two forms not recorded since the nineteenth century, are also sclerodistomids; but the descriptions of these taxa are incomplete. Eurycoelum sluiteri was described (Brock, 1886) from the stomach of Lutjanus sanguineus [= Diacope metallicus] off Java. The genus has been considered by certain workers, including Yamaguti (1971), to be a synonym of Hemiurus; but this is not the case. In fact it is possible that this genus may be a synonym of Prosogonotrema, which has been recorded from Lutjanus spp. on several occasions; but only an examination of the type-specimens, which It is 114 D. I. GIBSON & R. A. BRAY we have been unable to trace, or material from the type-host and locality can substantiate this. The situation with regard to Distoma gigas, a gigantic species from the stomach of Luvarus imperialis, has been discussed in detail by Gibson & Bray (1977). SCLERODISTOMOIDIDAE fam. nov. large; stout, elongate oval and attenuated anteriorly. Ecsoma absent. Body-surface smooth. Oral and ventral suckers well developed, small ventral sucker well inside anterior half of body. Body ; Prepharynx absent. Pharynx well developed. Oesophagus short. 'Driisenmagen' present. Gutcaeca sinuous; end blindly near posterior extremity, very close to stem of excretory vesicle (no union observed). Testes two; slightly lobate; symmetrical to oblique; in hindbody close to ventral sucker; pre-ovarian. Seminal vesicle tubular convoluted in forebody. Pars prostatica short; tubular with wide lumen. Ejaculatory duct short. Hermaphroditic duct short; present within small, cone-shaped permanent sinus-organ. Sinus-sac small and poorly developed or apparently absent. Genital atrium well developed. Genital pore mid-ventral at level of pharynx. Ovary oval; in middle of body; separated from testes by loops of uterus. Mehlis' gland postero-lateral to and uterine seminal receptacle present. Canalicular or blind seminal and Juel's organ absent. Uterus inter-caecal; coiled almost entirely in hindbody, in both pre- and post-ovarian fields; with narrow, convoluted descending loop reaching near to posterior extremity and convoluted ascending loop which is initially narrow and then much broader. Eggs small; numerous; without filaments. Vitellarium tubular; with two main collecting ducts situated medially, one anteriorly and other posteriorly oriented laterally directed dendritic branches present between testes and level a short distance anterior to posterior extremity. Excretory vesicle Y-shaped; stem short; arms initially in dorsal and ventral fields, pass laterally and ovary. Laurer's canal receptacle ; unite in forebody. Parasitic in gall-bladder of marine teleosts. COMMENT. it We have erected a new family for the genus Sclerodistomoides Kamegai, 1971, because from the accacoeliids in the structure of the pharynx, from the sclerodistothe absence of Manter's organ, and from both groups in the unique orientation of the differs significantly mids in main collecting ducts of the vitelline system. Its closest relative appears to be the accacoeliid genus Paraccacladium. SCLERODISTOMOIDES Kamegai, 1971 [T(w) ; t(s)] Defined as family. TYPE-SPECIES. Sclerodistomoides pacificus Kamegai, 1971 [by original designation]. COMMENT. Lintonius novikovi Baeva, 1965, does bear some superficial resemblance to Sclerodistomoides, but the description of this species by Baeva (1965) does not include enough data to confirm this. Yamaguti (1971) suggested that it might be a sclerodistomid. Family SYNCOELIIDAE Looss, 1899 Body elongate or dorso-ventrally flattened; usually with pedunculate ventral sucker. Ecsoma absent. Body-surface smooth, but commonly papillate on forebody and on peduncle, if present. Oral and ventral suckers well developed; may possess accessory suckers around their rim. Glandular cells common in subtegumentary parenchyma and within musculature of suckers. Pharynx well developed. Oesophagus short. Cyclocoel usually present, but gut-caeca may end blindly ( ?) or form a uroproct. Testes eleven to eighteen distinct, oval follicles (usually arranged in pairs), seven to eight transverse rows of small follicles, or just a large number of irregular pre-ovarian, in hindbody. Seminal vesicle thin-walled; tubular; winding or sinuous; in forebody. Pars prostatica tubular. Ejaculatory duct short. Hermaphroditic duct and genital atrium present, but indistinguishable when sinus-organ is absent. Permanent sinus-organ and follicles; sinus-sac present or absent. Genital pore mid-ventral in anterior forebody. Ovary post-testicular; composed of five large, oval, isolated lobes or numerous irregular follicles. Laurer's canal and THE HEMIUROIDEA 115 and canalicular or blind seminal receptacle be present. Uterus passes posteriorly but coils mainly in pre-ovarian hindbody. Eggs numerous, small, non-filamented. Vitellarium usually seven (occasionally five or six) isolated, oval lobes, or irregular acinous bunches or rows of follicles; post-ovarian. Excretory vesicle Y-shaped; arms united in forebody, may initially run in dorsal and ventral fields. Free floating metacercarial stage present. Parasitic in branchial and buccal cavities, on skin, in (?) oviduct and in (?) gut of elasmobranchs and marine teleosts. uterine seminal receptacle present. Juel's organ absent, but rudimentary seminal receptacle Key 1. may to Syncoeliidae A. B. Ovary numerous irregular follicles arranged in rows; vitellarium irregular acinous bunches or rows of follicles OTIOTREMATINAE (p. 115) SYNCOELIINAE (p. 116) Ovary 5 large isolated lobes; vitellarium 5 to 7 oval, isolated lobes . Subfamily SYNCOELIINAE Looss, 1899 Small accessory suckers around rim of suckers absent. Peduncle usually present. Cyclocoel present. Testes eleven to eighteen distinct, oval lobes; usually arranged in pairs. Permanent sinus-organ present or absent. Hermaphroditic duct and genital atrium present, but indistinguishable when sinus-organ is absent. Sinus-sac absent or rudimentary. Ovary composed of five large, isolated follicles. Rudimentary seminal receptacle may be present as proximal dilation of Laurer's canal. Uterus arranged in large, regular loops dorsally and ventrally to gonads. Vitellarium seven (occasionally five or six) small, isolated, oval lobes. Parasitic in branchial and buccal cavities (? with occasional records from gut) of sharks and marine teleosts. COMMENT. Our work with this group indicates that Syncoelium Looss, 1899, can be conveniently split into two distinct genera on the basis of the presence or absence of a sinus-organ (Gibson & Bray, 1977). When present, the sinus-organ is a well-developed structure, visible in sections and whole-mounts in both adults and metacercariae (see Gibson, 1976). In addition, in forms lacking a sinus-organ the genital atrium appears to be indistinguishable from the hermaphroditic duct, the hindbody tends to be spatulate rather than tubular, and the ventral sucker is somewhat less pedunculate. Furthermore, the latter forms have been recorded from the gills, whereas the forms possessing a sinus-organ usually occur in the buccal cavity and on the gill-arches. Key 1 . to Syncoeliinae A. B. Permanent sinus-organ absent hermaphroditic duct indistinguishable from genital atrium tendency for hindbody to be spatulate; ventral sucker normally sessile or on short peduncle; normally parasitic on gills SYNCOELIUM Permanent sinus-organ present; hermaphroditic duct easily distinguishable from genital ; ; atrium; hindbody usually tubular; ventral sucker usually on well-developed peduncle; usually parasitic in buccal cavity or on gill-arches COPIATESTES SYNCOELIUM Looss, 1899 Hindbody broad or spatulate. Ventral sucker sessile or surmounted on short peduncle. Permanent sinus-organ absent. Hermaphroditic duct indistinguishable from genital atrium. Parasitic on gills (? and in intestine) of sharks and marine teleosts. TYPE-SPECIES. Syncoelium ragazzii (Setti, 1897) [by monotypy]. COPIATESTES* Crowcroft, 1948 [n(w,s)] surmounted on well-developed peduncle. Permanent Hindbody duct and sinus-organ present. Hermaphroditic genital atrium easily distinguishable. Parasitic in elongate, tubular. Ventral sucker * It is also spelt Capiatestes in original publication, but this is a typographical error. 116 D. GIBSON & I. R. A. BRAY branchial (especially gill-arches and gill-rakers) and buccal cavities (?and intestine) of marine teleosts. TYPE-SPECIES. Copiatestes thyrsitae Crowcroft, 1948 [by original designation]. Subfamily Paronatrematinae Skrjabin OTIOTREMATINAE Skrjabin & Guschanskaja, 1957 & Guschanskaja, 1957 [proposed, but not named, by Dollfus (1950)]. [Paronatrema is poorly known.] Accessory suckers may be present around rim of suckers. Cyclocoel present (?or absent; caeca may end blindly or form uroproct). Testes numerous irregular follicles or seven to eight irregular transverse rows of follicles. Hermaphroditic duct present within sinus-sac (? not clearly described in Paronatrema). Permanent sinus-organ absent. Ovary composed of numerous irregular follicles which may be arranged in rows. Vitellarium irregular acinous bunches or rows of follicles. Parasitic in branchial cavity or on skin (? or in oviduct or intestine) of sharks and rays. Key 1. to Otiotrematinae A. B. Small accessory suckers present on oral sucker and/or ventral sucker PARONATREMA OTIOTREMA Small accessory suckers on suckers absent (papillae present within oral sucker) . OTIOTREMA Setti, 1897 [t(w,s)] flattened, alate, recurved. Papillae present within oral sucker; Forebody cylindrical; small accessory suckers within suckers absent; ventral sucker pedunculate. Gut-caeca sinuous in hindbody forebody; with numerous diverticulate outgrowths in hindbody; forming cyclocoel. Sinus-sac large, reaching close to dorsal surface. Ovary and vitellarium consisting of numerous acinous bunches of follicles, posterior to numerous follicular testes. Uterus in transverse coils; present in lateral fields of hindbody. Parasitic in branchial cavity ( ? or intestine) of sharks. TYPE-SPECIES. Otiotrema torosum COMMENT. We Setti, 1897 [by original designation]. have examined some of the material collected by Looss, and it appears to agree well with his description (Looss, 1899). PARONATREMA [This genus is Dollfus, 1937 poorly known.] Forebody sub-cylindrical; hindbody [t(w); n(w)] flattened, oval. Small accessory suckers present within oral and/or ventral suckers; ventral sucker large, but apparently not pedunculate. Gut-caeca sinuous; apparently end blindly (? or form uroproct or cyclocoel: interpretations uncertain). Testes consist of rows of follicles or segmented tubules. Ovary composed of irregular follicles (interpretations conflict). Vitellarium consists of rows of follicles or seg- mented tubules. Uterus numerous transverse or stomach of sharks and rays. coils in hindbody. Parasitic on skin or (?) in oviduct TYPE-SPECIES. Paronatrema vaginicola Dollfus, 1937 [by monotypy]. COMMENT. It would appear that in some descriptions the ovary and Mehlis' gland may have been confused. Generic Index to part Ml Acanthuritrema Accacladium Accacladocoelium 106 58 58 Accacoelium . Acerointestinecola Adinosoma ... 58 88 97 THE HEMIUROIDEA Aerobiotrema Ahemiurus Albulatrema . Allogomtiotrema Allostomachicola Allotangiopsis Anahemiurus . Anguillotrema Aphanhystera Aphanuroides Aphanurus Apoblema Aponurus Arnold Arnoldia Assitrema Atheria . Azygia Genarchopsis Genolinea Glomericirrus 61 Gomtiotrema Gonocerca 61 Halipegus 65 65 85 102 78 78 110 87 Hassallius 62 112 . Bilacinia 108 Botulus 99 1 02 94 64 Brachadena Brachyphallus Bunocotyle Caballeriana . 61 Guschanskiana Gonocercella Grassitrema . 61 Helaphanurus . Hemipera Hemiperina Hemiurus . Holacanthitrema Hydrophitrema Hypohepaticola Hysterolecitha Hysterolecithoides Isoparorchis Chauhanurus Chelatrema Chenia . 65 Laticaudatrema . 81 Lecithaster Clupenurus . Copiatestes . . Lampritrema . 92 90 Lecithophyllum Lecithurus 103 88 101 Derogenes Derogenoides Deropegus Dichadena 72 Leptosoma Lethadena Dinurus Dissosaccus . Distoma gigas 94 113 Dollfuschella Dollfustra vassosius 76 Duosphincter Ectenurus 66 87 83 90 89 . . Elongoparorchis Elytrophalloides Elytrophallus . Erilepturus Eurostomum Eurycoelum . . Follicovitellosum Genarchella Genarches . 83 61 100 98 102 Lecithochirium Lecithocladium Leptolecithum Dinosoma 92 90 Josstaffordia 83 106 82 97 86 101 Johniophyllum 94 Dictysarca 88 67 Jajonetta Cyatholecithochirium Cylindrorchis 73 78 105 105 70 . 94 92 78 110 89 115 . Intuscirrus Catarinatrema Ceratotrema . 91 Indoderogenes Indostomachicola 115 . 99 100 108 98 Hirudinelloides . Cladolecithotrema 65 75 75 85 Hirudinella 58 . 75 73 95 58 76 . . Capiutestes 78 67 90 . 87 77 85 77 61 . Bathycotyle Bhaleraoia 82 65 83 117 Leuceruthrus Leurodera Lintonius Liocerca 102 95 62 73 114 72 72 108 112 107 106 87 79 93 88 99 . Liopyge. Lobatovitellovarium Mabiarama Macradena . . Macradenina Magnacetabulum Magnibursatus Magniscyphus . Me coder us Mediolecithus Megadistomum 61 87 61 Merlucciotrema 96 Metahemiurus 85 113 Mimodistomum 61 108 Mitrostoma Mneiodhneria Monolecithotrema 67 58 76 74 . . . 70 118 D. Monorchiaponurus Monorchimacradena . Monovitella Mordvilkoviaster Musculovesicula . Myosaccium . I. GIBSON & 104 Prosterrhurus Proterometra 79 1 02 90 66 Pseudazygia Pseudobunocotyla Pseudodichadena Pseudodinosoma 107 Neogenolinea 66 85 93 68 . Neohysterolecitha . Neotheletrum Odhnerium Ophiocorchis Opisthadena Orophocotyle Orthoruberus 58 78 67 59 73 116 . . Otiotrema BRAY 107 Neodichadena Neohemiurus R. A. 88 Pseudosclerodistomoides Pseudostomachicola 111 Ptychogonimus Pulmovermis 111 . Qadriana Quadrifoliovarium Saturnius Sclerodistomoides Separogermiductus 88 78 85 Sterrhurus 96 67 59 76 87 . . Paronatrema 116 83 . Pelorohelmins Plerurus Plicatrium Profundiella 96 95 99 76 74 . Progenarchopsis Progonus Prolecitha Prolecithochirium 108 95 85 112 113 113 . Pronopyge Prosogonotrema Prosorchiopsis Prosorchis IV. A . Rhynchopharynx 60 Paraplerurus Parasterrhurus Paratetrochetus Paravitellotrema Parectenurus 67 107 95 78 110 Pseudogenarchopsis 61 Parahemiurus . Pseudolecithaster Otodistomum Parahalipegus 61 . Paraccacladium Paradinurus . 61 . . Sclerodistomum . Stomachicola Synaptobothrium Syncoelium Tangiopsis Tetraster Tetrochetus . Theletrum Thometrema . Thulinia Tricotyledonia Trifoliovarium Tubulovesicula Tyrrhenia Unilacinia Uroproctinella Uterovesiculurus Vitellotrema . Voitrema Xenodistomum 88 98 104 108 59 64 114 112 92 92 88 97 115 80 83 59 69 80 105 95 109 88 80 109 99 87 76 97 61 discussion on the evolution of the Hemiuroidea Evolutionary trends in the Hemiuroidea presentation of any evolutionary picture for the Platyhelminthes must remain hypothetical, as it is unlikely that there will ever be any fossil record due to the soft-bodied nature of these The animals. Possible evolutionary patterns can only be exposed by the knitting together of general morphological trends in organs, organ-systems and whole animals. Having distinguished a trend, there is the problem of deciding which way the trend is moving, and hence which is the primitive and which is the advanced condition. In addition, the possibility should not be forgotten that an intermediate form is primitive and that evolution is proceeding in two opposite directions. In order to assess which form is primitive, it is helpful to adopt the use of certain external indicators. As far as parasitic helminths are concerned useful indicators include: 1. The supposed 'primitiveness* of the host Although superficially it appears more likely that the more archaic and primitive vertebrates harbour more archaic and primitive parasites, this is not necessarily so. Owing to the variable THE HEMIUROIDEA 119 ecological factors involved, archaic hosts can harbour what appear to be 'advanced' parasites, vice versa. In addition, there are often widely differing opinions as to the relative ages of certain groups of vertebrates, and this tends to limit its value as an indicator. One might and expect, however, that a group of helminths restricted to birds would be more advanced than one restricted to elasmobranchs. Unfortunately, the vast majority of the hemiuroids are parasitic in fishes, and, although certain primitive groups are recognized, it is not known for certain whether elasmobranchs are more primitive than bony fishes (Osteichthyes). the hemiuroids only the azygiids appear to occur in fishes which are widely held to be primitive. Otodistomum commonly occurs in the shark Hexanchus and has been recorded from Amongst Chlamydoselachus and Heterodontus, and both Azygia and Leuceruthrus occur in the holostean Amia. Other groups occuring in elasmobranchs are the ptychogonimids and the syncoeliids, the Ptychogonimidae and the Otiotrematinae being entirely restricted to these hosts. Azygia has also been recorded from Acipenser, a member of primitive group Chondrostei; but little emphasis can be placed upon this result as Derogenes and several species of hemiurid have also been recorded from this host. This apparent mixture of what we believe to be 'primitive' and relatively 'advanced' forms is possibly associated with the migratory habit of sturgeons and the low degree of host-specificity exhibited by some of the more 'advanced' hemiuroids. There is also a single record of Halipegus from the related chondrostean Polyodon. Except for certain halipegine derogenids, which occur in amphibians and, rarely, in amphibious snakes, and the pulmovermine hemiurids, which are restricted to the lungs of sea-snakes, the remainder of the hemiuroids occur in teleosts. 2. The habitat of the host Parasites of aquatic vertebrates will tend to be more primitive than those from terrestrial vertebrates, because aquatic vertebrates tend to be more primitive than terrestrial vertebrates it is much easier to envisage the origins of parasitic platyhelminths in aquatic conditions. All the hemiuroids are parasitic in aquatic or amphibious hosts, the majority being parasitic in marine teleosts, but a few groups are commonly found in freshwater hosts. and because Unfortunately, there is no conclusive evidence to suggest that teleosts arose in freshwater, or vice versa, although a freshwater origin is preferred by some workers. It should be emphasized that any evidence based upon the habitat of the host should be treated with may have passed from fresh- to salt-water or from water to land, and back, on more than one occasion during the course of their evolution. caution, as various hosts the hemiuroids, only the azygiids and the halipegine derogenids are successful parasites of freshwater fishes, and only the isoparorchiids, a very small group, are restricted to these hosts. One interesting coincidence is that all three of the azygiid genera from freshwater fishes occur in Amongst North America, two being endemic, and that this is the only region of the world where holostean Another possible coincidence is that the majority of halipegine genera and the fishes survive. majority of isoparorchiid records occur in Asia, especially in the southern half of the continent: is the possible centre of evolution and radial dispersion of freshwater teleosts (see this location Darlington, 1957). 3. Host-specificity expect helminths with a high-degree of host-specificity to be more primitive than those with a low-degree. This is because it is likely that highly specific associations develop over a long period of time, and once they have arisen the further evolution of the parasite itself tends to be restricted to within the limits of the evolution of the host. This is a very general feature, however, and as digeneans tend to have a low degree of host-specificity with One might regard to their vertebrate host, it is of limited value. worth noting, nevertheless, that the host-range of the adult forms of certain groups and genera do tend to be restricted. The accacoeliines, with the exception of Tetrochetus, occur only in molid teleosts and the ptychogonimids appear to be entirely or almost entirely restricted to It is galeomorph sharks. Bathycotyle and Hirudinella parasitize scombroid and coryphaenid teleosts, 120 D. I. GIBSON & R. A. BRAY and Botulus and Lampritrema are usually restricted to Alepisaurus and Lampris, respectively. Prominent among other examples are the macradeninine and quadrifoliovariine lecithasterids, which occur only in acanthurid teleosts. Alternatively, many members of the Hemiuridae, Lecithasteridae, Bunocotylidae and Derogenidae appear to exhibit little or no host specificity amongst marine teleosts, although certain individual species or genera may appear to be highly host-specific. One species of Halipegus is reported to occur in freshwater teleosts and amphibians. The azygiids are present in freshwater teleosts, elasmobranchs, holosteans and rarely in chondrosteans, and although they appear to be restricted to certain groups of elasmobranchs, they appear to exhibit little host-specificity. of the above cases, e.g. the accacoeliines, that much of the apparent ecological rather than immunological or physiological, and it is likely that host-specificity ecologically based host-specificity has less evolutionary significance, as it would appear that an ecological restriction is a prerequisite for the development of other types of host-specificity. Our lack of knowledge of the life-history in many cases, however, prohibits the differentiation of these types. Nevertheless, the above examples do tend to illustrate the fact that there is a tendency for the successful groups, such as derogenids, hemiurids, lecithasterids and bunocotylids to exhibit in general a low degree of host-specificity, while the smaller groups, such as accacoeliids, hirudinellids, ptychogonimids, etc. tend to be more restricted. If our hypothesis that hostspecificity is acquired over a long period of association is correct, then it is likely that these smaller groups will tend to be more primitive than the larger. The azygiids occupy an anomalous position in that to some extent they are restricted to particular groups of fishes, but within these groups they are widespread. This might be explained by the fact that they are a small, but successful, group which occupy niches, i.e. the stomach of freshwater fishes and elasmobranchs, where It is obvious in many is competition from other digeneans 4. is severely limited. Related groups Undoubtedly the most important evidence can be taken from features common in groups which are held to be related to, and perhaps more primitive than, the group under study. Digeneans, monogeneans, cestodes and aspidogastreans are generally thought to have evolved from primitive rhabdocoel turbellarians, possibly similar to the Dalyellida, which inhabit the mantle-cavity or viscera of bivalves. Most authorities now agree that the Aspidogastrea is the closest relative of the Digenea, and Rohde (1971a) in an abstract states: may 'The Aspidogastrea are considered to be primitive, direct decendents of turbellarians, which are not yet closely adapted to parasitism and have not yet incorporated the vertebrate host as a fixed component in their life-cycle. They are closely related to the ancestors of the Digenea. Aspidogastrea and Digenea are both primarily parasites of molluscs.' In the same context Rohde (1971b) refers to the Aspidogastrea as 'living fossils'. It is likely, therefore, that features common to the Aspidogastrea and Digenea either must be primitive or are features produced by parallel or convergent evolution. Some primitive features may also be common in other parasitic platyhelminths and in the rhabdocoels; but, since these groups are successful, widely specialized and more distantly related, great care should be taken in the interpretation of any correlations, as the same features have undoubtedly been evolved independently by parallel and convergent evolution. Beklemishev (1964 [1969]), for example, states, when discussing the reproductive system of the Platyhelminthes 'In spite of the great : diversity of these adaptations, which appear independently in the various groups, the problems involved are repeatedly solved by similar methods, and that in animals far apart in the system.' When attempting to decide which of a group sion of trends which tend to flow in the is same primitive, one must, therefore, look for a succesdirection. It is unlikely, however, that one will encounter all of the trends proceeding 'satisfactorily' in the same animal. It is a fact that parallel and convergent evolution do occur, and each species is adapted to its particular niche rather than to illustrate an evolutionary picture. Parallel evolution is important because, as the members of the group originally shared the same gene-pool, the same mutations are likely to occur down the separate evolutionary branches, and thus the same features may evolve independently in several THE HEMIUROIDEA 121 different sub-groups. It is essential, therefore, that one looks at the overall trends in the group as a whole. This is especially important where the loss of organs may have occurred. In an attempt to show the evolutionary trends within the Hemiuroidea, we have followed three different organs and organ-systems in which definite trends do occur. These are: (1) the seminal storage and disposal apparatus in the female reproductive system; (2) the vitellarium; and (3) the terminal genitalia. Seminal storage and disposal apparatus in the female reproductive system. One of the most significant, but not one of the most obvious, trends in the Hemiuroidea is the development of the seminal storage and disposal apparatus, especially the latter, in the female system. In the majority of hemiuroids the proximal region of the uterus forms a seminal reservoir and is termed the uterine seminal receptacle. As a uterine seminal receptacle occurs in the Aspidogastrea (see Rohde, 197 la), it is likely that this condition is primitive in digeneans. Evidence from other platyhelminth-groups is difficult to interpret as they are specialized and involve, in the case of the Turbellaria, a vagina (copulatory canal) and several different types of seminal receptacle, and, in the case of the Monogenea and Cestoda, usually a vagina (or vaginae) with a dilation which forms a seminal receptacle. However, in some rhabdocoel turbellarians such as Mesostoma, a seminal receptacle in the form of a dilation of the oviduct does occur. Considering that the ovovitelline canal, which is the equivalent of the uterus in the Digenea, is short and that there is no Mehlis' gland, this feature is somewhat similar to a uterine seminal receptacle. As stated above, the sperm in the majority of hemiuroids is stored in the proximal region of the uterus. From the uterus small amounts of activated sperm pass through Mehlis' gland, where presumably fertilization of the ova usually occurs. Excess and spent sperm, plus excess vitelline material, are then disposed of via Laurer's canal, which in certain groups, e.g. the Azygiidae, Accacoeliidae and Hirudinellidae, connects the oviduct with the exterior via a dorsal pore (see Fig. 6; arrangement A). Such sperm and vitelline material in Laurer's canal can be seen in sectioned material: occasionally ova are also present. This process is naturally very wasteful, and it is apparent that certain turbellarians and monogeneans have developed an analogous duct, the genito-intestinal canal, which disposes of similar residues by transporting them into the gut, in order that this material can be re-processed. Our work has shown that some hemiuroids appear to have evolved a special organ, Juel's organ, within which this waste-material is degraded and re-absorbed. It is clear that this organ did not arise overnight, as traces of its development can be seen in present forms. In groups, such as Gonocercinae, Syncoeliinae and Isoparorchiidae, the proximal region of Laurer's canal is slightly dilated, forming a rudimentary seminal receptacle, within which excess spermatozoa and vitelline material are stored before passing along the remainder of the canal (see Fig. 6; arrangement B). Our observations suggest (1) is killed or stored until it dies, and that it may begin to disintegrate within the rudimentary seminal receptacle, before being passed along the canal. The distal part of the canal in these groups tends to be slightly glandular in nature, and the pore itself is often tightly that the excess material closed by a sphincter: thus, it is possible that some re-absorption may occur in these distal regions. In forms such as Derogenes and apparently Prosorchis, a rudimentary Juel's organ is found (see Fig. 6; arrangement C). In these cases the Laurer's canal does not open to the exterior, as the distal part of the duct is modified and forms an oval structure with a similar amorphous appearance to that of a fully-developed Juel's organ. During the course of evolution, Laurer's canal has become shorter, thus bringing the rudimentary Juel's organ and rudimentary seminal receptacle closer together. In Prosogonotrema these two structures are very close together (Fig. 4B). This process has continued until the rudimentary Juel's organ completely envelopes the rudimentary seminal receptacle, thus forming a complete Juel's organ (see Fig. 6; arrangement D). The enclosed rudimentary seminal receptacle has been known in the past as the 'inner vesicle' (Juel, 1889; Lander, 1904). A complete Juel's organ has been observed in Genarchopsis Rao, 1974), in (Anjaneyulu, 1968; Madhavi & Rao, 1974), Elongoparorchis (Madhavi numerous hemiurids, knowingly or unknowingly, by several authors, including Juel (1889) and Lander (1904), and by ourselves in various hemiurids, Hysterolecitha and Arnola. final deve- & A lopment, which appears to have occurred during the development of the Opisthadeninae, and B usr Fig. 6 Different arrangements of the seminal storage and disposal apparatus in the female [bsr, blind seminal receptacle; Jo, Juel's organ; Lc, Laurer's canal; rsr, rudimentary seminal receptacle; usr, uterine seminal receptacle.] reproductive system (see text), rJo, rudimentary Juel's organ; THE HEMIUROIDEA 123 probably the majority of the lecithasterids, is that the inner vesicle expands to fill Juel's organ, thus forming a blind seminal receptacle (see Fig. 6; arrangement E). The uterine seminal receptacle blind seminal receptacle tends to be a large, thick-walled structure, is lost in these groups. which is connected to the oviduct by a narrow duct: the sole remnant of the original Laurer's A canal. This final development presumably means that the spermatozoa pass through Mehlis' gland in the opposite direction to that which normally occurs in the remainder of the hemiuroids. Spent spermatozoa and excess vitelline material are, therefore, voided via, or broken down and re-absorbed by, the uterus. The evidence, which suggests that the presence of Laurer's canal opening to the exterior in conjunction with a uterine seminal receptacle is primitive, is that this is exactly the same~arrangement which occurs in the majority of aspidogastreans (e.g. Multicotyle, Lophotaspis, Cotylogasteroides, Macraspis}. The development of a seminal and vitelline disposal organ, however, is not limited to the Juel's organ of some hemiuroids. It appears that analogous structures may have developed in an aspidogastrean and certain turbellarians. Stafford (1896) described Laurer's canal of Aspidogaster conchicola Baer, 1826, as ending blindly in the form of a 'thick-walled bulb', and Voeltzkow (1888) refers to the same structure as a 'receptaculum vitelli' because it appeared to contain vitelline residues.* The absorption of excess sperm by the Turbellaria is discussed by p. 31). He notes that, in addition to the genito-intestinal canal which occurs in some groups, there appear to be several different organs involved: these include the 'vesicle of Lang' of the polyclads (see Bock, 1927), the 'vesicula resorbiens' of the Kalyptorhynchia, and the copulatory bursa, which is found in many turbellarians. It is clear that, while there is a need to dispose of excess and spent seminal and vitelline material, there is in free-living helminths a strong selective pressure for the development of an organ of re-absorption, which de Beauchamp (1961, thus aids the animal's economy. Owing to the ready availability of food, this pressure is probably much less in the parasitic forms, as demonstrated by the number of digeneans which still use Laurer's canal as a seminal and vitelline drain, but it would still appear to be advantageous to the economy of the parasite for it to develop a less wasteful system. If the actual biology of these digeneans is examined in detail, it is clear that many hemiuroids are stomach-parasites, and that they have developed mechanisms which protect them from the low pH and, in the case of marine Gibson, 1970; Gibson, 1971). teleosts, the high osmolarity of the environment (MacKenzie The hemiurids which live in such conditions apparently withdraw their ecsoma and contract, with the result that they are protected by their thick tegument, and the derogenids from the stomach tend to migrate anteriorly towards the oesophagus during periods of low pH or high osmolarity. These parasites, therefore, contrary to intestinal forms, do not appear to be in a & position to feed at all times. It would seem, consequently, that it is advantageous for these parasites to re-utilize some of its waste-material in order to help maintain egg-production during when feeding is limited. The presence of a structure resembling a rudimentary periods Juel's organ in Aspidogaster conchicola does suggest that Juel's organ may also be a primitive feature; but this structure appears not to have been observed in other aspidogastreans. In addition, it appears that a similar structure may be present in digeneans unrelated to the hemiuroids, e.g. Styphlodora bascaniensis Goldberger, 1911 (see Goldberger, 19116), and Cyclocoelum sharadi Bhalerao, 1935 (see Madhavi & Rao, 1974), and that this feature has not apparently been reported in other species of these genera whica have been examined. It would seem, therefore, that a distal modification of Laurer's canal, which appears to be associated with the degradation of seminal and vitelline material, has been independently evolved on at least four different occasions. This would appear to vindicate Beklemishev's statement quoted above. Only in the hemiuroids, however, does this organ appear to have developed further, i.e. past the 'rudimentary' stage, and only in the hemiuroids is it common to entire groups. In other instances, * Voeltzkow claimed to have seen the canal as the animal matured. Stafford, however, the oviduct. it appears to have been developed independently by open to the exterior in young animals, and that the 'receptacle' developed was of the opinion that Laurer's canal developed as an outgrowth from 124 D. I. GIBSON & R. A. BRAY species, possibly recently, to meet their present ecological requirements. This is supported fact that none of the latter species are gut-parasites, and, therefore, such a development by the would probably be economically advantageous. Many digeneans have lost Laurer's canal, or have altered its function, i.e. in some groups it is used as a vagina. The latter occurrence we consider to be an advanced feature (Gibson & Bray, 1975), and species which use this method of copulation (one sided, as opposed to the possibility of reciprocal copulation where the genital atrium is used) normally have a thin-walled canalicular seminal receptacle, formed as a proximal dilation of Laurer's canal, and no uterine seminal receptacle, e.g. Diphterostomum bmsinae (Stossich, 1889) and Haploporus benedeni (Stossich, - see Palombi (1931). We should emphasize that remarkably few digeneans have ever been 1887) seen in the act of copulation. Assuming, from the above evidence, that the presence of Laurer's canal opening dorsally and a uterine seminal receptacle are, in the Hemiuroidea, primitive characters, it is not unreasonable to presume that Juel's organ has evolved in the manner described above. The derivation of the blind seminal receptacle of the opisthadenines and the majority of the lecithasterids from Juel's organ is not so obvious. If one discounts the possibility that it arose independently as a diverticulum of the oviduct, there appears to be only one other alternative. That is, its independent derivation from the rudimentary seminal receptacle. In the Lecithasteridae, Trifoliovarium has a large, functional canalicular seminal receptacle which has presumably evolved directly from a rudimentary seminal receptacle. The blind seminal receptacle of the related Cladolecithotrema has presumably evolved by the loss of Laurer's canal. Alternatively, in Hysterolecitha and presumably Hysterolecithoides Juel's organ is present. The blind seminal receptacle of the remainder of the lecithasterids could, therefore, have evolved from either a rudimentary seminal receptacle or Juel's organ. As the inner vesicle of Juel's organ appears to have been derived from the rudimentary seminal receptacle, this is essentially the same thing; but the thick, fibrous wall of the blind seminal receptacle is quite different to the relatively thin-walled type of seminal receptacle which usually occurs in digeneans. This suggests that the wall of the blind seminal receptacle may be derived from the outer capsule of Juel's organ. There is also evidence that the blind seminal receptacle of the opisthadenines has evolved from Juel's organ of the hemiurids and, as discussed below, that a similar blind seminal receptacle appears to have arisen independently from Juel's organ in the Didymozooidea. Although the form of the seminal storage and disposal system tends to be relatively constant within a family or subfamily, there is a notable exception to this. In the Derogenidae a variety of conditions occur: (1) many halipegines, such as Halipegus, possess Laurer's canal, which opens dorsally, and a uterine seminal receptacle; (2) other forms, such as the Gonocercinae, afe similar except that a small, but distinct, rudimentary seminal receptacle occurs; (3) in the remainder of the halipegines, such as Genarchopsis [but see p. 79] and Arnola, a fully developed Juel's organ is present and (4) in the derogenines a continuous variation of conditions occur (a) Derogenes possesses a large rudimentary seminal receptacle containing spermatozoa which is connected by Laurer's canal to a rudimentary Juel's organ (b) in Progonus the rudimentary seminal receptacle is further enlarged to function as the only seminal store, the uterine seminal receptacle being lost, and the rudimentary Juel's organ is present at the junction of the seminal receptacle and Laurer's canal, which ends blindly; and (c) in Leurodera Laurer's canal and the rudimentary seminal receptacle appear to have been lost, leaving a blind seminal receptacle. The variation which occurs in this group can perhaps be explained by the fact that it is a large, successful group, possibly with primitive origins, arising at about the time when the first variations of the primitive seminal storage and disposal apparatus, such as the development of Juel's organ, were beginning to occur. It is possible that parallel evolution is responsible for some of the conditions which occur in this group and their apparent similarity to the arrangements in other hemiuroid groups. : ; ; Vitellarium. There appears to be a very clear trend in the form of the vitellarium in the Hemiuroidea. Briefly, commencing with a follicular form, and passing through tubular and sevenlobed stages, the vitellarium is finally reduced to two, or occasionally one, oval masses. The trend begins with the follicular vitellarium which occurs in the Azygiidae (Fig. 7; arrangement A). (2) THE HEMIUROIDEA B Fig. 7 Different arrangements of the vitellarium (see text). 125 126 D. I. GIBSON & R. A. BRAY follicles become linked together along the collecting ducts, thus giving a chain-like appearance, as occurs in the syncoeliid Otiotrema and to some extent in the accacoeliid Tetrochetus (Fig. 7; arrangement B). The vitellarium then becomes distinctly tubular, consisting of many long, often convoluted, tubules, which may be branched (Fig. 7 arrangement C). The latter type These ; of vitellarium occurs in the Accacoeliidae, Hirudinellidae and Isoparorchiidae. The next stage is that the number of tubules, which are usually unbranched, is reduced to seven: these usually being arranged with three on one side of the body and four on the other (Fig. 7 arrangement D) e.g. some sclerodistomids and some hemiurids, such as Dinurus and Stomachicola. The length of the seven tubules is then gradually reduced, so that they pass through digitiform (e.g. Lecitho; ; cladium, Plerurus, Ectenurus), tear-shaped (e.g. Elytrophallus, Lecithaster, Hysterolecitha) and oval (Prolecitha, Dichadena, Lecithophyllum, Syncoelium) stages (Fig. 7; arrangement E). The seven lobes, whether tubular, digitiform, tear-shaped or oval, may form a rosette arrangement, with three lobes on one side and four on the other, or may form two separate groups of three and four lobes which are connected by the collecting ducts. Presumably from the latter arrangement have developed forms, such as Dinosoma and Arnold, with two vitelline masses which are distinctly three- and four-lobed (Fig. 7; arrangement F). The lobation then tends to be almost or entirely lost (e.g. Hemiurus, Brachyphallus), resulting in forms, such as Derogenes, Lethadena and Myosaccium, with two totally unlobed, oval masses. In genera such as Bunocotyle, Monolecithotrema, Monovitella and Chenia the vitellarium is present as a single entire or slightly lobed mass (Fig. 7; arrangement G). This mass was probably, and almost certainly in the latter two cases, formed from the fusion of two oval masses but there is a possibility that it could be the result of either the loss of one mass or the condensation of a rosette-arrangement. It must be emphasized here that the above is only a general trend in the form of the vitellarium, ; is a certain amount of variation within each group, particularly within the hemiurids and the lecithasterids. For example, a relatively common feature of the lecithasterids is a doubling of the number of vitelline lobes. In addition, the number of vitelline tubules or lobes, commonly seven in many of the hemiuroids, is variable, six, eight or nine frequently being reported. The presence of nine (four and five) lobes is especially common on the two vitelline masses of the as there halipegine derogenids. As the various links in the above pattern do appear to illustrate the trend relatively clearly, the only real problem is to find evidence which indicates that the follicular arrangement of the vitellarium is primitive. It appears, however, that a follicular vitellarium is found in the majority of monogenean and cestode groups, in all aspidogastreans and also in some rhabdocoel turbellarians, e.g. Mesostoma. This suggests very strongly that the follicular arrangement is primitive. It is likely that the duplication of the vitelline glands, resulting in the follicular arrangement, occurred as an early development to accommodate an increase in egg-production. This would have been especially necessary when the 'ancestral rhabdocoel' became an obligate parasite. This 1907, which is emphasized by evidence from the digenean Schistosoma mansoni Sambon, indicates that thirty to forty vitelline cells are present in each egg (Gonnert, 1955). The widespread spacial arrangement of this highly metabolically active organ-system in the 'primitive' is probably a mechanism to aid the absorbtion of nutrients from the surrounding parenchymatous tissue, rather like the roots of a tree. Even though food is often continually available to the 'primitive' hemiuroids, such as the azygiids and hirudinellids, they tend to be rather large for digeneans, and, therefore, still have certain problems with regard to the diffusion forms of nutrients. The more 'advanced' hemiuroids tend to be smaller in size, and, therefore, there is no longer such a need for a widespread follicular, dendritic or simple tubular vitelline system, as the problems associated with the diffusion of nutrients are reduced. In addition, there is more competition for space, as the uterus tends to take up a much greater proportion of the body. This latter factor, plus the economic advantage in reducing the distance involved in the transthe vitellarium to a small portation of vitelline material, adequately explains the reduction of masses. rosette or to one or two One apparent contradiction is the vitelline structure of the syncoeliine syncoeliids, which, as it consists of seven oval lobes, indicates that it is far more 'advanced' than the remainder of the THE HEMIUROIDEA 127 anatomy. The premature reduction in the size of the vitellarium can be explained, however, by certain modifications in the process of egg-formation which appear to occur in this group. Our observations suggest that the eggs of Copiatestes are produced in a uterine ob'type (see glossary), have a membranous 'shell' and contain only one, or a very small number, of vitelline cells. During the egg's passage down the uterus the vitelline cell(s) appear to replicate many times, the membranous 'shell' permitting the diffusion of nutrients into the egg as a source of material and energy for this process. Not until a full complement of vitelline cells is present, at about the middle of the uterus, does the egg-shell become thicker, tanned and hardened. The demand on the vitellarium for vitelline cells appears, therefore, to be greatly reduced, possibly by a factor Some aspects of egg-shell formation have been described by Gibson of twenty to thirty times. (1976) for Copiatestes filiferus (Leuckart, in Sars, 1885) and by Coil related Syncoelium spathulatum Coil Kuntz, 1963. & & Kuntz (1963) for the Terminal genitalia. The terminal genitalia of the Hemiuroidea show a great number of modifications; but do in fact, with a small number of exceptions, illustrate one basic trend. There are, however, a number of variations in the general pattern, and it is likely that some features of this trend have been evolved independently by parallel evolution. In order to understand both the nature of the trend and the variation, we must first examine the function of these structures. The function of the male terminal genital apparatus is that of ejecting spermatozoa and enabling it to enter the female system, either of another worm or of the same individual. The function of the female terminal genitalia is that of ejecting eggs into the environment, and, we suggest in the case of the Hemiuroidea, receiving spermatozoa from the male terminal genitalia of either another worm or of the same individual. As indicated above, it is clear from our studies of Laurer's canal (Gibson & Bray, 1975) that in the Hemiuroidea, when this duct is present, it functions as a seminal and vitelline drain, not as a vagina (Trifoliovarium may be an exception). Evidence from the work of Nollen (1968), who used 3 H-thymidine-labelled spermatozoa in Philophthalmus megalurus (Cort, 1914) suggests that cross-insemination occurs in the majority of cases whenever possible but that, when only single worms are present in a host, self-insemination occurs regularly. Nollen also noted that labelled spermatozoa disappeared from the uterine seminal receptacle within fourteen to sixteen days of copulation, which indicates that repeated insemination is required. It would appear, therefore, that self-insemination is a mechanism which has evolved to enable lone specimens in a host to produce fertile eggs. It seems very likely that in some genera self-insemination has become increasingly important, to the extent that the male copulatory apparatus has atrophied. In some cases, such as Bathycotyle, Gonocerca, Aerobiotrema, Syncoelium (sensu stricto) and Tetrochetus, where the copulatory apparatus has completely disappeared or has been reduced to a vestige, they must, it appears, rely solely upon self-insemination. It is likely that the latter phenomenon has occurred independently in several different groups both within and outside the Hemiuroidea. To illustrate this point, the terminal genitalia and the seminal storage and disposal system of the opecoeline opecoelids are almost identical to those which occur in Gonocerca. Too much systematic importance, therefore, should not be placed upon the absence or reduction of the copulatory apparatus. The main trend in the structure of the terminal genitalia of the Hemiuroidea appears to be as follows. It commences as a simple sinus-organ, produced as a protrusion of the base of the genital atrium, and containing both of the simple, tubular male and female ducts. These ducts come together and unite near the summit of this organ, forming a short hermaphroditic duct which opens via a terminal pore. The close proximity of the male and female ducts which opens into a common genital atrium aids both reciprocal cross-insemination and self-insemination, and, similarly, the development of an hermaphroditic duct further facilitates self-insemination. This latter arrangement (Fig. 8; arrangement A) occurs in the azygiids, where the sinus-organ is a highly contractile, permanent structure, but is usually found in a relatively contracted state. The sinus-organ of the azygiids, which presumably acts as a copulatory organ and possibly aids the extrusion of eggs through the genital pore, is formed from the proximal region of the wall of the genital atrium, and it uses its own intrinsic musculature for extension and contraction. The genital atrium presumably serves as a vagina during copulation, and it is likely that the muscular 3. ; 128 D. I. GIBSON & R. A. BRAY B SO ss H aso [aso, Different arrangements of the terminal genitalia (see text), Fig. 8 amuscular sinus-organ; hd, hermaphroditic duct; so, muscular sinus-organ; ss, sinus-sac.] THE HEMIUROIDEA 129 its wall forces the spermatozoa, deposited during copulation, back into the hermaphroduct through the aperture of the contracted sinus-organ. Following on from the type A arrangement, the sinus-organ becomes a relatively larger structure in its contracted state, and some of its intrinsic musculature begins to concentrate into a thin, diffuse sac-like structure surrounding its base (Fig. 8; arrangement B). At the same time, the hermaphroditic duct tends to lengthen, usually reaching at least to the base of the sinus-organ. This arrangement can be seen gradually developing in Prosorchis, Copiatestes, Isoparorchis, Sclerodistomum, Accacoelium and Prosogonotrema, resulting in a type C arrangement (Fig. 8) where the diffuse, muscular thickening at the base of the sinus-organ, which is referred to as the sinus-sac, becomes more apparent in the latter four examples, and, in addition, the intrinsic musculature of the sinus-organ itself tends to become slightly reduced. We consider that the sinus-sac aids the extrusion of the sinus-organ by exerting hydrostatic pressure upon its contents (Gibson & Bray, 1974). Many of the derogenids tend to have an arrangement very similar to that of Prosogonotrema, except that the cone-shaped sinus-organ tends to be small. In the dinurine action of ditic hemiurids the sinus-sac is better developed (Fig. 8 arrangement D), becoming an enlarged oval or tubular structure with a thick, muscular wall, and the sinus-organ is usually cone-shaped, often with a slight reduction in its intrinsic musculature. The sinus-organ may be large, as in Paradinurus, or small, as in Dinurus, and it should be mentioned that in a small number of dinurines, such as Stomachicola, the sinus-organ is absent or reduced to a rudiment: in the latter cases the sinus-sac is also reduced in size. It is noticeable that at about the stage of the type D arrangement, the seminal vesicle, which until now has normally been tubular, tends to become more saccular and often develops sphincters and thus becomes partitioned. These appear to be modifications caused by the fact that, during ejaculation, the spermatozoa now have to be forced into the hermaphroditic duct against the hydrostatic pressure produced when the sinus-sac ; aids the eversion of the sinus-organ. The next stage (Fig. 8 arrangement E) is that the intrinsic musculature of the sinus-organ is then lost, resulting in the fact that it must be entirely everted by hydrostatic pressure. This arrangement can be seen in the Elytrophallinae and in the Glomericirrinae, especially in the former, where the sinus-organ appears to be almost totally amuscular, the sinus-sac is well developed and the seminal vesicle is surrounded by an extremely thick muscular wall. The latter structure is presumably necessary because of an increased hydrostatic ; pressure necessary to evert the sinus-organ. In the next stage (Fig. 8 arrangement F) the genital atrium is reduced in size and a permanent sinus-organ is lost. The latter is replaced by a short, temporary sinus-organ, rarely seen in fixed specimens, which is formed by evagination of the ; hermaphroditic duct under hydrostatic pressure. As the hydrostatic pressure is less than that required in the type E arrangement, because of the much smaller sinus-organ and genital atrium, pressure is usually exerted on the seminal vesicle by sphincter muscles or by a thin, muscular layer in its wall, rather than by a thick, muscular wall. This arrangement occurs in the Hemiurinae, Lecithochiriinae, Stomachicola and a small number of related dinurines, the Opisthadeninae, the Lecithasterinae and the Quadrifoliovariinae. Finally, in the Hysterolecithinae, Trifoliovariinae, Lethadeninae, Plerurinae, Macradenininae, Dictysarcinae, Prolecithinae and Gonocercinae, the sinus-sac is gradually atrophied (Fig. 8; arrangement G) until in genera such as Aerobiotrema lost completely (Fig. 8; arrangement H). Presumably, as mentioned above, the ability to cross-inseminate becomes reduced and is finally lost altogether. groups It is worth noting that there is a slight deviation within the Hemiuridae, in that the Glomericirrinae, with the type E arrangement, and the Lecithochiriinae, with the type F arrangement, have and Gonocerca, it is in the latter developed an ejaculatory [prostatic] vesicle. This appears to be a modification of the ejaculatory duct, the function of which is not known for certain. It may, however, form a temporary storage organ as part of a mechanism for ejecting larger quantities of spermatozoa during each ejaculation. If this is true, then the glandular cells, which often line it, may function, with regard to the stored sperm, in the same way that the pars prostatica does to normal quantities of sperm passing duct during ejaculation. the Hirudinellidae, stand out as being totally distinct from the remainder of the hemiuroids in that they possess a 'cirrus-sac'. This structure almost certainly developed independently of the sinus-sac; but it does appear to be analogous. The reason why such a structure through this One group, 130 D. I. GIBSON & R. A. BRAY has developed in this group is probably because its ancestors lost, or did not develop, an hermaphroditic duct, with the result that the copulatory organ ('cirrus') did not contain the female duct. In this group, therefore, both the male and the female ducts have developed their own finger-like projections from the wall of the genital atrium. It seems certain that the 'cirrussac' of the hirudinellids is not homologous with the cirrus-sac which is found in many other groups of digeneans. At first sight, it is somewhat difficult to see how the hirudinellid arrangement could have evolved from the type A arrangement; but other morphological features of the hirudinellids suggest a relatively close affinity with some of the other 'primitive' hemiuroids. For this reason, it seems unlikely that the hirudinellids split away very early in hemiuroid evolution before the development of an hermaphroditic duct. It is possible, however, to envisage the gradual separation of the male and female ducts of the type A arrangement, where the hermaphroditic duct is short, much in the same way as appears to have occurred in some species of Halipegus, where the two ducts open separately at the end of the sinus-organ. It is very unlikely that the Hirudinellidae resemble the ancestral form of the hemiuroids, as it is difficult to imagine how an hermaphroditic duct could have been derived from the hirudinellid arrangement. We can assume that the presence of apparatus well adapted to enable cross-insemination to occur is the primitive condition in the hemiuroids, as cross-insemination occurs in all other groups of helminths. Even in the primitive hemiuroids, however, it is almost certain that selfinsemination does occur, and Dawes (1946) notes that self-insemination of lone specimens of the aspidogastrean Aspidogaster conchicola has been observed. It seems likely that the type A arrangement in our trend is primitive. It is a fact that the majority of hemiuroids differ from the majority of helminths in that the copulatory organ is not the usual cirrus, which is often enclosed by a cirrus-sac. Nevertheless, all of the structures termed 'cirrus' are not homologous, as the copulatory organs of many groups of animals have a phallic appearance. In addition, it is unlikely that all of the structures termed 'cirrus-sac' are homologous, as similar 'sacs' surround the base of, and are associated with the protrusion of, many eversible organs, e.g. the proboscis sac of the Acanthocephala. If we examine the aspidogastreans, the majority of species do possess a cirrus-sac, but several do not. There appears to be no evidence in the latter group for the presence of an hermaphroditic duct. As it seems difficult to envisage the development of an hermaphroditic duct, similar to that occurring in the hemiuroids, from a form with a cirrus-sac, it is possible that the rhabdocoel-like ancestors of the digeneans possessed a temporary penis-papilla ('cirrus'), lacking a penis-bulb ('cirrus-sac'), which was formed from the wall of the genital atrium. Commencing with such a structure, it is possible to envisage the development of all of the variations of the terminal genitalia which occur in the Digenea and Aspidogastrea. A suggested evolutionary scheme within the Hemiuroidea Published works on evolution within the Digenea are few. Aspects of this subject have been discussed by workers such as Odening (1974), and detailed comments on particular groups have Maillard (1974); but only a few workers, such been given by others, such as Bayssade-Dufour as Poche (1926) and Cable (1974), appear to have indicated detailed evolutionary relationships within the Digenea as a whole. The majority of evidence in the more recent work has come from & As discussed in our introduction, we believe such information is questionable. Admittedly data from upon the intra-molluscan stages are likely to be of some value, but only at the higher taxonomic levels, and, as indicated on p. 38, there are some anomalies. If, as Rohde (1972) suggests, the cercariae were 'invented' by the digenean ancestors as a mechanism to aid the transmission from the molluscan host to the vertebrate host, evidence based upon cercarial morphology, especially as this larval stage is more susceptible to environmental changes than the others, is somewhat dubious. Although the majority of phylogenetic hypotheses on the evolution of and within the Digenea have been based upon larval characteristics, there is evidence that workers are beginning to reappraise the value of adult morphology. Powell & Sogandares-Bernal (1970), for instance, stated: 'While on the subject of larval trematodes, the systematic value of comparative anatomical studies of the terminal genitalia and sensory structures of adult worms should be emphasized. larval that morphology and much of details of the life-history. the evidence based THE HEMIUROIDEA 131 Homologies and analogies of terminal genitalia (for example in the Hemiuroidea) should prove useful in determining phylogenetic relationships.' Using evidence outlined in the trends illustrated above, we have attempted to build a hypothetical picture of the evolution of the Hemiuroidea. Our proposed relationships are expressed We believe that the most primitive groups are the azygiids and the ptychogonimids, and in Fig. 9. that the most closely related of these to the ancestors of the remainder of the hemiuroids appear to be the leuceruthrine azygiids. These groups exhibit a combination of primitive characters, such as a follicular vitellarium, a sinus-organ without an accompanying sinus-sac and with Laurer's canal acting as a seminal and vitelline drain. The Leuceruthrinae, which appears to exist as a single species, possesses the same gonadal arrangement as that which occurs in the vast majority of the remainder of the hemiuroids. Another interesting feature which may indicate primitiveness group is that in known azygiid life-cycles the cercariae are eaten directly by the definitive host. This suggests the possibility that the azygiids evolved before the acquisition of the second intermediate host which occurs in most digenean life-cycles. Other primitive groups are the in this Hirudinellidae, Bathycotylidae, Isoparorchiidae, Syncoeliidae, Accacoeliidae it seems likely that they, especially the latter four, have arisen moididae, and and Sclerodistofrom a common ancestor. Nevertheless, there are features of the syncoeliids, such as the presence of seven which suggest that they are more advanced than indicated by vitelline lobes in the syncoeliines, the position which we have allocated to them in our 'evolutionary picture'; but, as discussed above (p. 126), these anomalies can be explained. In the latter groups a sinus-sac develops (a 'cirrus-sac' in the case of the hirudinellids) and the vitellarium becomes tubular. In our opinion the remainder of the hemiuroids have evolved from an ancestor resembling the present-day sclerodistomids, although most probably lacking Manter's organ and with more posteriorly situated gonads. From this ancestral form, which presumably possessed a vitellarium consisting of seven tubules, a well-developed sinus-organ and sinus-sac, and Laurer's canal (which although opening dorsally was on the point of evolving a rudimentary Juel's organ), four main lines appear to have evolved. These are: (1) the modern members of the Sclerodistomidae; (2) the Derogenidae; (3) the Lecithasteridae, Dictysarcidae and the Didymozooidea (see p. 133); and (4) the Hemiuridae and Bunocotylidae. The development of Juel's organ, in the rudimentary and or the fully developed form, has occurred in all of these groups. As forms with Laurer's canal opening dorsally also occur in three of the groups, it seems more likely that Juel's organ has arisen independently by parallel evolution than by the concurrent evolution of forms with and without this organ in all of these three groups. The sclerodistomids are the only one of these groups which either have not developed a complete Juel's organ or in which no members of the group possessing such an organ survive, although rudimentary forms occur in Prosogonotrema and Prosorchis. It would appear that despite the position of the gonads, the prosogonotrematine and prosorchiine genera are perhaps more closely related to the other three groups outlined above than the sclerodistomines. The Derogenidae are a very successful group with a complex mixture of primitive and advanced features, especially with regard to the nature of the seminal storage and disposal apparatus in the female reproductive system. Nevertheless, the majority of members tend to be relatively similar in gross morphology, although it seems likely that the three subfamilies of this group separated quite early in the evolution of the group. They probably owe their success to the fact that they tend to fill niches where competition is somewhat reduced, i.e. the stomach of oceanic fishes, in the case of the Gonocercinae and the Derogeninae, and both the stomach of brackish water and freshwater fishes and the mouth and eustachian tubes of amphibians, in the case of the Halipeginae. The Lecithasteridae appear to have evolved via forms similar to Trifoliovarium, but still retaining a uterine seminal receptacle and a rudimentary seminal receptacle. From this form developed the modern members of the Trifoliovariinae and, after the independent formation of Juel's organ, the Hysterolecithinae. The remainder of the lecithasterids could have evolved from forms similar to Trifoliovarium by the loss of Laurer's canal, much in the same way as Cladolecithotrema has probably developed but it seems more likely that they have evolved from hysterolecithine ancestors. This is suggested by the great morphological similarity between the ; 132 D. Fig. 9 A I. GIBSON & R. A. BRAY suggested evolutionary tree for the Hemiuroidea. THE HEMIUROIDEA Hysterolecithinae and some of the other 133 and because the thick-walled nature of of the lecithasterids suggests that it might have evolved lecithasterids the blind seminal receptacle in the rest Juel's organ by hypertrophy of the 'inner vesicle'. from It is also apparent, because of the presence of Juel's organ and other morphological similarities, that not only the Dictysarcidae, but also the Didymozooidea (see below), may have evolved from hysterolecithine ancestors. In the largest group, the Hemiuridae, an ecsoma in association with a plicated tegument appears to have developed (see p. 41), although the former is occasionally reduced and the latter is often completely lost. These adaptations appear to be associated with the hostile habitat of the majority of hemiurids, the stomach of marine teleosts which is a region of variable pH and osmolarity. The most primitive group appears to be the Dinurinae, some of which have features in common with some of the modern sclerodistomids, although all appear to possess a fully developed Juel's organ. The dinurines probably gave rise to the elytrophallines by the development of an amuscular sinus-organ and associated changes in the seminal vesicle. The elytrophallines could then have given rise to: (1) the Glomericirrinae, by the development of an ejaculatory (prostatic) vesicle, which in turn gave rise to forms, such as the Lecithochiriinae, by the loss of a permanent sinus-organ; and (2) the Hemiurinae and the Lethadeninae, by the loss of a permanent sinus-organ. The Bunocotylidae appear to have evolved from ancestral hemiurines by the loss of the ecsoma. It is worth noting that some members of the Aphanurinae still retain a plicated tegument. In the members of the Bunocotylinae, which are extremely small, Juel's organ appears to have been lost, there apparently being no obvious mechanism for disposing of excess seminal and vitelline material. It is possible that these compact and apparently advanced worms not only space, but also spermatozoa and vitelline material, more efficiently, thus such a specialized organ. In the opisthadenines Juel's organ appears to have the value reducing into a blind seminal receptacle, much in the same way as we suggest it developed in developed utilize the majority of the lecithasterids. Throughout the evolution of this group it is clear that there is a general decrease in body-size, ranging from the giant azygiids and hirudinellids to the minute bunocotylids. Associated with a more of body-space, such as the development of a of excess reproductive products. In addition, although less certain, there appears to be an increase in the proportion of the body occupied by the uterus, and an increase in the dependency upon self-fertilization, thus reducing the need for large and complex terminal genitalia. this decrease in size is compact vitellarium, Some comments on efficient utilization and a more efficient utilization the relationship of the Didymozooidea and the Paramphistomoidea to the Hemiuroidea The Didymozooidea are a group which several early workers, such as Odhner (1907) and Poche (1926), considered to be evolved from hemiuroid stock. This early work was based upon adult morphology. Baer & Joyeux (1961), however, basing their hypothesis on the work of Ishii (1935) which indicated that adults of this group developed directly from eggs, recognized the Didymozoidea as a new subclass, distinct from the Digenea, within the class Trematoda. Recently Cable (1955, 1974), using evidence from larval stages, has reiterated Odhner's initial hypothesis that this group is derived from hemiuroid stock. Skrjabin (1955) and Yamaguti (1971) present the didymozooids as a distinct suborder and superfamily, respectively, to the hemiuroids, but do not comment on any relationship between the two. If those didymozooid genera with a simpler and more conventional morphology, such as Nematobothrium van Beneden, 1858,* are examined, several similarities with the hemiuroids are apparent. The testes are normally pre-ovarian and the ovary normally occurs anterior to the vitellarium. The male and female terminal ducts fuse, often forming a short hermaphroditic duct, and open via a common genital pore, and in some instances a small terminal papilla not unlike a sinus-organ is present. In addition, the shape and arrangement of the gonads in juvenile speci- mens of Didymocystis acanthocybii Yamaguti, 1938 * The conception of the genus used here is that of Yamaguti (as figured (1971). by Yamaguti, 1970), are very 134 D. I. GIBSON & R. A. BRAY More convincing, however, are the present in Nematobothrium robustum Yamaguti, 1970, and that Odhner (1907) has described what appears to be a well-developed Juel's organ in the closely related N. scombri (Taschenburg, 1879) (Fig. 10A). Although the latter structure in Nematobothrium spp. has usually been referred to as a seminal receptacle, Yamaguti (1970), similar to those of the dictysarcid hemiuroid Elongoparorchis. facts that a uterine seminal receptacle is when describing Neonematobothrioides poonui, noted that it contained germ-cells and vitelline material, in addition to spermatozoa. An apparent Juel's organ was also seen by Dollfus (1935) in Nematobothrium pelamydis (Taschenburg, 1879). Juel's organ of the didymozooids appears to differ slightly from that in the hemiurids, for example, in that the 'inner vesicle' is not completely enclosed proximally by the outer region of the organ, suggesting that it is perhaps slightly more primitive (see p. 121). The presence of Juel's organ and a uterine seminal receptacle, however, does not appear to be the usual condition in the more highly developed didymozooids. In the majority of these cases the uterine seminal receptacle has apparently been lost and Juel's organ appears to have become transformed into a blind seminal receptacle, which is connected to the oviduct by a short duct, much in the same way as blind seminal receptacles have probably been in the majority of lecithasterids and the opisthadenine bunocotylids. In sections of an formed [close to Didymocystis Ariola, 1902] from Katsuwonus pelamys off the outer half of the blind seminal receptacle has a thick wall, possibly being the vestige of the outer region of Juel's organ, and the inner half (that closest to the duct) of this seminal receptacle has a thin wall, possibly being formed from the part of the 'inner vesicle' not unidentified didymozooine Papua New Guinea, enclosed by the outer region of Juel's organ (Fig. 10B). These observations on the gross morphology and on the nature of the seminal storage and disposal apparatus in the proximal female reproductive system of certain didymozooids suggest to us that this group did evolve from hemiuroid stock close to the origins of the Dictysarcidae probably from an ancestral form of hysterolecithine lecithasterid (see Fig. 9). B bsr t Parts of the seminal storage and disposal apparatus two didymozooids: A. Nematobothrium scombri (modified Fig. 10 didymozooine. the female reproduction system of Odhner, 1907); B. Unidentified after blind seminal receptacle; eiv, external 'inner vesicle'; organ; tw, thick-walled region of blind seminal receptacle.] [bsr, vesicle'; Jo, Juel's in w iiv, internal 'inner THE HEMIUROIDEA 135 worth noting that there are certain morphological features which suggest that there between the paramphistomoids and some of the more primitive hemiuroids. These include a follicular vitellarium, the absence of a prepharynx, paired testes which are usually pre-ovarian, the presence of Laurer's canal in association with a uterine seminal receptacle and It is also be may affinities terminal genital apparatus. The paramphistomoids differ fundamentally in adult morphology only in the fact that the excretory pore is dorsal rather than being terminal. Although the hindbody is almost absent in this group, there is also a tendency for its reduction in certain hemiuroids, especially in the Sclerodistomidae. The paramphistomoids are generally considered to be stomach parasites of terrestrial vertebrates: several genera have, however, been recorded from similar One particular group, the Brumptiidae Stunkard, 1925, appears to be morphologically very similar to the hemiuroids in that its members possess a well-developed sinus-sac and an hermaphroditic duct, and, in the lateral fields, there is a distinct hindbody present in the form of teleosts. somewhat similar to, but smaller than, those which occur in the syncoeliid Otiotrema. workers such as Dawes (1936) have considered the paramphistomoids to be very Although primitive, Cable (1974) places this group well up one of the branches of his evolutionary tree. He also places it on quite a distinct branch to the hemiuroids, although Poche (1926) had placed them much closer together. Evidence from adult morphology suggests that the paramphistomoids might have been derived from hemiuroid stock close to the point where the syncoeliids and hirudinellids evolved. Nevertheless, there does appear to be fundamental differences in the morphology of the larval stages and the life-history which tend to preclude any serious consideration of this relationship until the significance of these differences is fully understood. lobes, being Acknowledgements We would like to take this opportunity of thanking the following people who have helped us with various aspects of this work: Mr T. Bakke (Zoologisk Museum, Oslo), Dr I. Ball (University of Amsterdam), Professor A. Brinkmann Jr (University of Bergen), Dr A. V. Gaevskaja Parasitological Museum, Tokyo), Dr R. Professor P. Nasir (Universidad de Oriente, (USDA, Maryland), Venezuela), Professor O. Nybelin (Natural History Museum, Gothenburg), Dr R. Overstreet (Gulf Coast Research Laboratory, Ocean Springs, Mississippi), Dr M. H. Pritchard (H. W. (AtlantNIRO, Kaliningrad), Dr Lichtenfels S. Kamegai (Meguro Beltsville, Manter Laboratory, University of Nebraska) and Mr J. Thulin (University of Gothenbuig). We Mr D. W. Cooper and Mr S. J. Moore for the preparation of many hundreds of sections, to Mrs H. Sabo for translating various Russian papers and to Miss J. S. Williams are also indebted to for help with the final copies of the illustrations. References Acena, S. P. 1947. New trematodes from Puget Sound fishes. Trans. Am. microsc. Soc. 66 127-139. Agrawal, V. 1966. Studies on some trematode parasites of fresh water fishes of Lucknow. Annls Parasit. hum. comp. 41 217-231. Ahmad, J. 1977. Two new species of digenetic trematodes of fishes from the Bay of Bengal. Neth. J. Zool. 27 305-309. Amato, J. F. R. 1968. Contribuicao ao conhecimento da fauna helmintologia do Rio Grande do Sul. novo parasito de peixe cascudo Plecostomus commersoni (Cuv. & Val.) (Trematoda, Hemiuroidea). Revta bras. Biol. 28 433-438. Anjaneyulu, G. 1968. Observations on the female reproductive system of Genarchopsis punctati Agrawal, 1966. Indian J. Helminth. 19 118-121. Ariola, V. 1902. Contribute per una monografia dei Didymozoon. I. Didymozoon parasiti del tonno. Archs Parasit. 6 99-108. Ataev, A. M. 1970. Description of Monovitella cyclointestina gen. et sp. n. and some remarks on the taxonomy of the family Halipegidae. Zool. Zh. 49 1465-1470. (In Russian; English summary.) Baer, J. & Joyeux, C. 1961. Classe des trematodes (Trematoda Rudolphi). In: Grasse, P. P. [Ed.], Trait e de zoologie, Paris, 4 561-692. Baer, K. E. von. 1826. Sur les entozoaires ou vers intestinaux. Bull. Sci. not. Geol. 9 123-126. : : : Um : : : : : : 136 D. GIBSON & I. R. A. BRAY Baeva, O. M. 1965. [Helminth fauna of Cololabis saira from the Pacific Ocean.] In: Leonov, V. A. el al. [Eds] [Parasitic worms of domestic and wild animals], Akad. Nauk SSSR, Vladivostok 33-42. (In : Russian.) Harrington, E. J. fishes, W. Academic 1957. 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