L JOURNAL SIZE, OF CRUSTACEAN BIOLOGY, 17(Z): 217-226, 1997 DISTRIBUTION, AND SIGNIFICANCE OF CAPITULAR OCTOLASMIS (CIRRIPEbIA: POECIi;A’SMATIDAE) Harold : ?S,..,’ K. Voris and William PLATES IN B. JeJScries ABSTRACT All adult Octolasmis live permanently fixed to animate hosts by a basal attachment disc. The peduncle connects the disc to the plated capitulum. The area of the capitular plates and the capitular perimeter bordered by plates is assessed for 28 species of Octobsmis. A, hypothesis that the species of Octolasmis that live inside decapod gill chambers will have smaller, more variable plates than those species that live on the exposed external surface of their hosts is articulated and tested. The data support the hypothesis under general conditions and also reveal an array of special circumstances suggesting that several aspects of host morphology and habits may also impact on the intensity of selection on capitular plate size and distribution. Within the superorder Thoracica Darwin, 1854, the order Pedunculata Newman, 1987, includes the superfamilies Praelepadoidea Chernyshev, 193 1; Heteralepadoidea NilssonCantell, 1921; Scalpelloidea Pilsbry, 1916; and Lepadoidea Darwin, 185 1 (see Anderson, 1994). The families of the Lepadoidea (Lepadomorpha) are differentiated on “. . . presence or absence of, degree of development, and number of capitular plates . . . ” (Zullo, 1982). Within the Lepadoidea, the approximately 60 species of the family Poecilasmatidae are relegated to the genera Octolasmis (28[+]), Trihsmis (1 [+I), Temnaspis (9[+]), Megalasmu (14[+]), and Poecilasma (3[+]) (Zevina, 1982). Species of Octolusmis are primarily associated with other living creatures such as corals, echinoderms, mollusks, crabs, lobsters, isopods, horseshoe crabs, fishes, and sea snakes (Jeffries and Voris, in press). Adult Octolusmis depend on these hosts as substrata and perhaps for protection and nutrition. This paper attempts to explore relationships among the variations in calcareous plates that occur on the surface of the capitulum of Octolusmis and their possible functions. Until now anatomical observations and only anecdotal references to the relationship of plate variation and function exist in the literature on the species. For example, it was reported that 0. indubia Newman, which lives more exposed, e.g., on the moutbparts of the host, has a capitulum which is more completely plated than is the case with 0. Zowei (Darwin), which lives protected in the gill chamber of the host (Newman, 1961). The speculation has been that robust capitular plates afford protection to species like 0. tridens (Aurivillius) and 0. wurwickii Gray that occur on exposed parts of the host carapace and appendages, whereas the host gill chamber affords protection for 0. ungulutu (Aurivillius) which has reduced capitular plates (Foster, 1987). We assert that the calcareous plates have two primary functions: protection and support. The purpose of this paper is to quantify the surface area that the capitular plates cover individually and collectively in relationship to the lateral surface area of the capitulum, to estimate the amount of the peripheral region of the capitulum that is supported by plates in species of Octolusmis, and to combine these measures with information on the host associations of each species to test the hypothesis that plates are reduced, and/or more variable, among species living in the protected microhabitats. This hypothesis evolved as follows: if the calcareous plates afford species of Octolusmis protection from abrasion and predation by shielding the capitular tunic and the soft parts therein, larger plates will provide more coverage and protection of the capitulum. Thus, those species of Octolasmis most in need of protection (e.g.; most exposed to predation and abrasion because of their locations on their hosts) will have the largest plates. Some species of Octolasmis may have acquired protection from abrasion and predation through the selection of host species with attributes such as large size, secretive life style, or venomous structures that offer special protection, Such species of Octolasmis would be expected to have less of their capitula covered by plates than would those selecting 217 ** 218 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 17, NO. 2, 1997 of the capitulum should be observed among those species exposed to less turbulence. This argument also implies that the arrangement of large plates covering most of the capitulum was acquired very early in the evolution of the Pedunculata and that the absence or reduction of plates in Octolusmis is a secondary loss. This is suggested by the fact that five (2 scuta, 2 terga, and carina) chitinous capitular plates were associated with some of the earliest members of the suborder Praelepadomorpha (order Pedunculata), a group represented in the Carboniferous by Pruelepas jaworskii Chernyshev (193 1) (see Schram, 1982). In addition, some evidence suggests that a pair of chitinous plates may have been present since the Silurian, when the genus Cyprilepas (suborder Cyprilepadomorpha) was commonly associated with the exoskeleton of eurypterids (Wills, 1963). TERGUM 1 MM Fig. 1. Line drawing of Octolasmis Zowei illustrating the location and shape of the three capitular plates measured in this study. hosts affording little such protection. It would also be expected that those species of Octolusmis selecting protected sites on their hosts (e.g., within decapod gill chambers) will have less of their capitula covered by plates than those species selecting exposed sites. We predict that in each of the above cases, variability in plate size will be highest in those species that have the least plate coverage. This prediction follows from the proposition that selection pressure to maintain plates for protection is relatively relaxed among those species that live in circumstances that afford protection by other means. An additional prediction is that plate reduction will be at a minimum among those forms that live on the external surface of their hosts in the shallow photic zone where potential visual predators abound. All species of Octolasmis are suspension feeders that depend on currents to bring food to them and the cirral fan to capture it. It is likely that feeding activity requires some capitular structural support. If the calcareous plates provide structural support to the capitulum, it follows that species exposed to stronger currents and turbulence will have plates that provide greater amounts of support. Conversely, diminished structural support MATERIALS AND METHODS The capitulum of poecilasmatid barnacles is typically characterized by 5 external calcareous plates: the paired scuta bordering the aperture and the distal end of the peduncle; the paired terga on the more distal border of the aperture; and the fifth plate, the carina, which forms a supporting spine adjoining the halves of the capitulum (Anderson, 1994). Figure 1 shows the location of these plates on the cosmopolitan species 0. lowei. Using an ocular micrometer, the capitular lengths and capitular widths of all specimens were measured and recorded in mm. The capitulum is often irregular in thickness and surface contour. However, with the aid of a camera lucida, 2 planar drawings were made of each specimen, 1 view from the left side and 1 from the right. Usually, each view depicts 1 scutum, 1 tergum, and the portion of the carina visible from that view. Octolasmis collare Jeffries, Voris, and Yang has a collar rather than 2 terga, but the collar measurements were placed under the terga designation for computational and comparative purposes. A Keuffel and Esser Number 620005 planimeter was used to measure the areas of the plates and the capitulum on the drawings in mm*. A Keuffel and Esser map measurer was used on the drawings to determine the total perimeter of the capitulum as well as linear segments of the capitular perimeter bordered by plates, and recorded in mm. One female mangrove crab, Scylla serrata (Forsk&l) (carapace width = 96.5 mm), collected at Singapore in June 1983, provided a large series of Octolasmis angulata and 0. COT(Aurivillius) from the same gill chamber (Jeffries et al., 1991). The fact that large series of both species were available on a single crab minimized variability that might otherwise be due to differences among crabs in terms of size, capture location, etc. The exact attachment sites of all of the barnacles on the gills of the crab were noted as each barnacle was removed and pre- I VORIS AND JEFFRIES: CAPITULAR Table 1. The 28 species of Octolasmis included in this study are listed alphabetically, along with their sample sizes. The means, standard deviations (SD), and ranges of capitular lengths are given in mm. Those species in permanent whole mount slides are indicated by an asterisk. Octolasmis angulata is represented by two samples and Lepas ansertfera is included for comparative purposes. Capitular Number 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. americanum aneulata a&lata* antiguae aperta avmonini brevis bullata* californiana carpilii* clavula collare* 0. 0. Q. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. dawsoni forresti geryonophila grayii hawaiense hoeki indubia lowei mtilleri neptuni orthogonia scuticosa tridens 0. car 0. uncus 0. warwickii 0. weberi Lepas ansertfera Mean 1 8.29 19 2.40 13 1.57 2 4.29 11 1.98 10 6.88 4 1.54 4 1.64 4 4.04 9 2.30 4 5.08 22 1.59 20 2.53 5 2.29 11 2.95 61 2.21 10 4.53 9 4.18 3 2.96 5 1.43 10 3.29 10 2.62 10 1.43 2 9.87 11 3.48 10 2.56 2 3.58 10 6.06 4 6.47 14 11.59 length (mm) SD oY4 0.39 0.14 0.25 1.12 0.41 0.66 1.36 0.71 0.94 0.21 0.43 0.14 0.63 0.66 0.67 1.87 0.83 0.34 0.29 0.23 0.25 0.20 0.66 0.25 0.43 0.74 1.40 3.82 Minimum Maximum 1.72 1.15 4.15 1.43 4.86 E 300 2.60 4.43 2.29 8.15 1.90 2.40 5.58 3.15 6.15 1.86 3.28 2.43 4.00 4.15 5.86 6.15 3.43 1.86 4.00 2.86 1.86 10.00 5.01 2.86 4.00 7.15 7.87 19.34 2157 0.86 4.00 1.00 1.57 2.15 2.15 1.00 3.72 1.00 2.00 1.14 2.86 2.15 1.14 9.72 2.29 2.15 3.15 5.00 5.01 5.00 served. Later, each barnacle was measured and drawings were made of the right and left sides of the capitulum. Of the total 140 0. car (capitular length range = 1.43-3.00 mm), a subset of 61 was selected for the plate study. Of the total 88 0. angulata (capitular length range = 2.14-3.43 mm) a subset of 65 was selected. By this selection of individuals a balanced representation of all the available size classes was obtained. Area and perimeter measurements were made from the drawings of each of the barnacles in these subsets. Some species used in this study were collected from decapods and sea snakes obtained in southeast Asia over a period of years beginning in 1981 (Jeffries et al., 1982, 1984, 1988, 1989). From these collections, 10 specimens each of 0. grayii (Darwin), 0. neptuni (MacDonald), 0. tridens, and 0. warwickii were selected for measurement and drawing. In addition, 10 0. mtilleri (Coker) which came from Callinectes sapidus Rathbun from Beaufort, North Carolina (Jeffries and Voris, 1983); 14 Lepas anserifera Linnaeus collected near Phuket, Thailand; and various museum specimens, including 0. americanum Pilsbry, 0. antiguae (Stebbing), 0. aperta (Aurivillius), PLATES 0. aymonini (Lessona and Tapparone-Canefri), 0. brevis Pearse, 0. californiana Newman, 0. clavula Hiro, 0. a’awsoni Causey, 0. forresti (Stebbing), 0. geryonophila Pilsbry, 0. hawaiense Pilsbry, 0. hoeki (Stebbing), 0. indubia, 0. Zowei, 0. orthogonia (Darwin), 0. scuticosa Hiro, 0. uncus Peruse, and 0. weberi (Hoek) were also selected for measurement and drawing (Table 1). All were preserved whole specimens, of which temporary aqueous mounts were made between a cover glass and slide. Drawings were made from these mounts, and the area and perimeter measurements were made on the drawings as outlined previously. Three species obtamed in Singapore and Malaysia as a result of previous work, 0. bullata (Aurivillius), 0. carpilii Rosell, and 0. collare (see Jeffries et al., 1982), were available only on permanent microscope slides. To compare the effects of preparation techniques on the drawings and measurements made therefrom, permanent slides of 0. angulata were also prepared. RESULTS Intraspecific I 219 IN OCi-OL4SMIS Variation in Samples and Measurements Bilateral Comparisons.-Comparisons of the measurements and the percentage calculations for the left and right sides of the capitulum were made in both 0. angulata and 0. col; both of which were represented by large samples. In 0. angulata, the mean capitular area, carina area, scutum area, and capitular perimeter were all larger on the left side than on the right side. The differences in capitular areas between the left and right sides (left side = 57.40 mm*, SD = 11.49 versus right side = 56.60 mm*, SD = 10.76) proved to be significant (t = 2.62, d.j = 64, P < O.Ol), as were the differences between the areas of the scutum on the left and right sides (left side = 4.43 mm*, SD = 1.04 versus right side = 3.74 mm*, SD = 0.84; t = 8.75, d.J = 64, P c 0.001). In 0. col; both the mean capitular area and the mean scutum area were larger on the left side than on the right side, but only the differences between scutum areas of the left and right sides (left side = 7.94 mm*, SD = 4.13 versus right side = 7.28 mm*, SD = 3.54) proved to be significant (t = 2.95, d.j = 60, P < 0.01). The data for these intraspecies left and right side comparisons met both normality and equality of variances criteria required by the t-test. In no case was the right side significantly larger than the left side in either 0. angulata or 0. COT. In 0. angulata, the mean percentage area of the capitulum covered by both the carina and the scutum was larger on the left side than on the right side. The difference in per- ., 220 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 17, NO. 2, 1997 Table 2. For two species of Octohmis the mean, standard deviation (SD), and coefficient of variation (CV) are given for the percentage of capitulum perimeter supported by plates, and the percentage of area of the capitulum covered by the carina, the scutum, and the two plates combined. 0. agnulafa (h’ = 65) Percentage of capitulum Meall SD Supported Carina area Scutum area Both mates area 54.39 2.15 1.18 10.53 6.66 0.58 1.43 1.76 0. cor(h’=61) cv 12.24 21.09 18.38 16.71’ centage covered by the scutum was significant (left side = 7.79%, SD = 1.43 versus ’ right side = 6.66%, SD = 1.10; t = 8.14, Ir_ld.J: = 64, P c O.OOl), as was the same comparison within 0. car (left side = 21.28%, SD = 6.57 versus right side = 19.76%, SD = 5.91; t = 3.03, d.$ = 60, P < 0.01). Although the above documentation of asymmetry is new for OctoZasmis, it is not unique among pedunculate barnacles (Anderson, 1994). These observations of asymmetry led us to make all comparisons described below using measurements from the left side of the capitulum only. Size or Ontogenetic Efsects.-To test for possible effects of barnacle size on the relative amount of area covered by the carina and scuturn, we compared groups of the smallest and largest barnacles. We compared a group of 13 small 0. anguhtu (- capitular length = 2.24 mm, SD = 0.07, range = 2.14-2.29) to a group of 17 large 0. angulatu (- capitular length = 3.11 mm, SD = 0.16, range = 3.00-3.43), and a group of 17 small 0. car ( - capitular length = 1.77 mm, SD = 0.12, range = 1.43-1.85) to a group of 15 large 0. car (- capitular length = 2.75 mm, SD = 0.15, range = 2.57-3.00), using the KolmogorovSmirnov two-sample test. The percentages of areas of the capitulum covered by the carina in the large and small 0. anguhtu, and in the large and small 0. car were not significantly different. The percentages of areas of the capitulum covered by the scutum in the large and small 0. angulutu also were not significantly different, but large 0. car showed significantly larger percentage coverage of the capitulum by the scutum than did the small 0. car (P < 0.05). This latter observation suggests that the various plate configurations and shapes that are typical of each species may, at least in some cases, be a result of differential growth rates of the plates and the capitulum, which in turn emphasizes the im- Mi%l SD cv 68.01 5.96 21.28 21.25 5.29 2.20 6.57 7.90 7.18 36.91 30.87 28.99 portance of using relatively homogeneous samples of similar-sized adults to represent each species when making interspecific comparisons. Interspecific Comparisons Octolasmis angulata and 0. car.-Relatively large samples of 0. angulata (65) and 0. car (61) obtained from the same gill chamber of a single crab (Jeffries et al., 1991) provided the opportunity to examine levels of variation in our measurements and to make statistical comparisons between the two species. For 0. angulatu and 0. car, Table 2 provides the ranges and standard deviations of the percentage of the capitular perimeter supported by plates, and for the percentage area of the capitulum covered by the carina, the scutum, and the two plates combined. In all of these percentages, 0. angulata and 0. car differ significantly from each other (KolmogorovSmirnov two-sample test, P < O.OOl), and 0. car is the more variable of the two species in these characteristics. For example, the coefficients of variation for the percentage of capitular coverage by the scutum for 0. angulatu and 0. car were 18.4 and 30.9, respectively. Multiple Species Comparisons Plate Areas.-The percentages of capitular surface covered by the carina, scutum, and tergum for 28 species of Octolasmis and one species of Lepas are presented in Fig. 2. For purposes of comparison, the 29 Octolasmis (28 species with 0. angu2atu present twice) were ranked in ascending order according to the percentage of total plate coverage of the capitulum. Within the 28 species of Octolasmis, this percentage of coverage ranged from about 7% in 0. bullata to 71% in 0. tridens. For comparison, Lepas ansergera from Thailand represents the extreme, where plates cover the entire capitulum. The contribution that each plate makes to the total percentage coverage varies among . VORIS AND JEFFRIES: CAPITULAR .= % PERIMETER PLATES IN OCTOLASMIS 221 SUPPORTED 100 0 Fig. 2. The mean percentage of the left capitular area covered by the carina, scutum, and tergum is shown for 28 species of Octolasmis and Lepas anserifera. Octolasmis angulata is represented by two samples. The species are listed in ascending order of percentage of plate coverage. Measurements (rnrn) on species designated with an asterisk were taken from drawings based on whole-mount slides. species. The percentage coverage by the carina ranges from zero in 0. bullata to 17 in 0. orthogonia. The coverage by the scutum ranges from 5% in 0. gray ii to 48% in 0. tridens, and the coverage by the tergum is zero in several species that lack the tergum entirely (e.g.,O. angulata, 0. bullata, and 0. cor), and as much as 22% in 0. americanum. of the capitular area covered is low, the peripheral position and narrow shape of the plates provide high levels of support. For example, the percentage of the capitular area covered is as low as 7% in 0. bullata and 9% in 0. angulata (slide mounts), whereas the percentage of the perimeter supported for these two species is 79 and 51 %, respectively. Perimeter Supported.- The percentage of the capitulum perimeter that is supported by plates is presented for each species in Fig. 2. This percentage was as low as 43% in 0. collare and complete (100%) in four species: 0. dawsoni, 0. orthogonia, 0. indubia, and 0. hoeki. Although there is a correlation (r = 0.69, P < 0.001) between the percentage of the perimeter supported and the percentage of total plate area, it is noteworthy that the percentage of the perimeter supported does not fall below 43% among the species studied. This is because, even when the percentage Coefficients of Variation.- The degree of intraspecific variation that occurs in plate shape and size differs from species to species and may reflect the intensity of natural selection on these structures. There is a significant inverse correlation (r = -0.70, p < 0.001) between the percentage of the capitulum covered by plates and the size of the coefficient of variation (Fig. 3). These results support the prediction that selection on the amount of plate coverage and perhaps the amount of support required is more relaxed among those species with relatively smaller plates. 222 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 17, NO.2, 1997 ~ ::) -.J ::) t: 0.. « O u.. O w (!J ~ w > 0 o ~ Fig. 3. The mean percentage of the left capitular area covered by capitular plates and its coefficient of variation are given for 28 species of Octolasmis. The species are in ascending order according to percentage of plate coverage. Literature Data.- Table 3 provides capitular support and plate area percentages on nine additional species of Octolasmis. These percentages are based on measurements made on individual drawings found in the literature. Although it is worth noting that all the percentages observed in this group fall within the ranges set by those taxa that we measured (Figs. 2, 3), the fact that these data are based on single drawings made by other investigators means that they are not directly comparable to our own data. Table 4 presents a list of all species of Octolasmis in alphabetical order for which we made original drawings and measurements (Table I) as well as those based on drawings from the literature (Table 3). For each species, its host category, its location on the host, and the usual water depth of the host are provided. DISCUSSION In Fig. 4, 28 species of Octolasmis are ordered, according to the mean percentage of the left capitular area covered by the capitular plates. The shading of the bars designates those species that are usually found in crustacean gill chambers (black), always found on the external surface of crustaceans (black with pattern), or on hosts for which there is some qualifying circumstance (white with pattern). Figure 4 suggests a strong but not absolute relationship between mean percentage of plate coverage and location on the host. Species that live their adult lives within the gill chambers of decapods have low percentages (7% for 0. bullata) to intermediate (30% for 0. brevis) of their capitula covered by plates. Those species that live on the exposed external surfaces of their crustacean hosts have relatively high percentages (43% and 71% for 0. warwickii and 0. tridens, respectively) of their capitula covered by plates. Thus, the prediction that plates will cover more area of the capitulum in species that live on externally exposed sites, compared to species living hidden inside gill chambers, is ten- VORIS AND JEFFRIES: CAPITULAR PLATES IN 223 OCTOLASMIS Table 3. Comparable data taken from the literature for nine additional species of Octolasmis. The capitular length and width measurements (mm) of the specimens are taken from literature sources. The percentages are based on measurements (mm) made on single published illustrations of either the left (L) or right (R) sides. Specimen Species of Ocrolasmis 0. 0. 0. 0. 0. 0. 0. 0. 0. alata (R) bathynomi (L) iloiloensis (L) nierstraszi (L) pellucida (R) sinuata (R) trigona (R) tydemani (L) versluysi (L) Capitular length Pementages Capitular width Capitulum supported i:: i:; 1.: 2’6 2’3 100.0 100.0 87.5 E 2:5 1.8 5.9 2:9 if3 0:8 3.6 80.8 89.3 89.3 100.0 94.1 Carina area Tergum area TOtal plate area 39.0 43.7 26.9 16.2 11.8 18.4 19.2 21.0 13.4 10.2 10.7 16.5 8.5 !5 lo:o 16.5 13.8 61.8 67.1 61.3 55.7 27.6 24.2 31.3 47.9 38.8 11.0 5.1 21.2 18.6 7.5 6.4 10.7 14.9 16.5 tatively supported by an array of species. We surmise that the plates afford significant protection from predation and abrasion for those species that live on exposed surfaces. from drawings Scutum , area Literature source Aurivillius, 1894 Annandale, 1909 Rosell, 1967 Hoek, 1907 Darwin, 185 1 Aurivillius, 1894 Aurivillius, 1894 Hoek, 1907 Hoek. 1907 The coefficients of variation of the mean percentage of the capitulum covered by all plates provide further support for this interpretation. If total plate coverage of the ca- Table 4. Host category, location on host, and water depth of host gleaned from the literature for 37 species of Octolasmis. Those species in permanent whole mount slides are indicated by an asterisk. Host category Location on host Depth Reference 0. 0. 0. 0. 0. 0. alata americanum angulata antiguae aperta aymonini decapods unknown decapods decapods decapods decapods gill chamber unknown gill chamber and mouthparts gill chamber gill chamber gill chamber shallow deep(>300m) shallow shallow shallow deep+300 m) 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. bathynomi brevis bullata* californiana carpilii* clavula collare* car dawsoni forresti geryonophila grayii hawaiense hoeki iloiloensis indubia lowei miilleri neptuni nierstraszi orthogonia pellucida scuticosa sinuata tridens isopods decapods decapods decapods decapods decapods decapods decapods isopods decapods decapods sea snakes decapods decapods decapods decapods decapods decapods decapods horny coral horny coral sea snakes decapods decapods decapods deep (>300 shallow shallow shallow shallow shallow shallow shallow deep (>300 shallow deep (>300 shallow deep (>300 shallow shallow deep (~300 shallow shallow shallow shallow deep (>300 shallow shallow shallow shallow 0. 0. 0. 0. 0. 0. trigona tydemani uncus versluysi warwickii weberi decapods animate decapods unknown decapods horny coral pleopods gill chamber gill chamber gill chamber protopodite of cheliped maxillipeds gill chamber and moutbparts gill chamber pleopods gill chamber and mouthparts gill chamber body and paddle tail gill chamber gill chamber and mouthparts gill chamber mouth parts gill chamber gill chamber gill chamber stems and branches stems body and paddle tail antenna and mouthparts gill chamber gill chamber, mouthparts, and carapace gill chamber external gill chamber unknown carapace and appendages stems shallow shallow shallow shallow shallow deep(>300m) m) m) m) m) m) m) Aurivillius, 1894 Pilsbry, 1907 Aurivillius, 1894 Stebbing, 1895 Aurivillius, 1894 Lessona and TapparoneCanefri, 1874 Annandale, 1909 Pearse, 1947 Aurivillius, 1892 Newman, 1960 Rosell, 1967 Hiro, 1936 Jeffries, Voris, and Yang, 1988 Aurivillius, 1892 Causey, 1960 Pilsbry, 1907 Pilsbry, 1907 Darwin, 1851 Pilsbry, 1907 Wells, 1966 Rosell, 1967 Newman, 1961 Darwin, 1851 Coker, 1902 MacDonald, 1869 Hoek, 1907 Darwin, 185 1 Darwin, 185 1 Hiro, 1939 Aurivillius, 1894 Aurivillius, 1894 Aurivillius, 1894 Hoek, 1907 Pearse, 1947 Hoek. 1907 Gray,’ 1825 Hoek, 1907 224 JOURNAL OF CRUSTACEAN BIOLOGY, VOl 17,NO.2, 1997 80 ~ :) -.J :) != Coo « () u.. O w ~ 60 inside gill chamber 40 ~ w 6 () 20 ~ 0 Fig. 4. The mean percentage of the left capitular area covered by the capitular plates is shown for 37 species of Octolasmis (see Table 1). The species are listed in ascending order of percentage of plate coverage. For each species of Octolasmis, the usual location on its host (Table 4) is indicated by shading. The intermediate condition, "qualifying circumstances," refers to a variety of situations that are elaborated in the discussion. pitulum is less important to species that live in protected situations, plate variability would be expected to rise as a result of relaxed selection. The relationship found between coefficients of variation and the mean percentage of the capitulum covered by plates supports this interpretation. In fact, we have observed an 0. miilleri and an 0. neptuni both lacking a tergum on one side, and another 0. miilleri and three 0. neptuni lacking both terga. Thirteen of the 28 species depicted in Fig. 4 are designated as having a qualifying circumstance associated with their host. For example, 0. gray ii is among those species that have the least plate coverage (11.7%), although it liyes exposed on the external surface of its host. However, it lives only on highly venomous sea snakes. We propose that the nature of these hosts may deter predators and thus reduce the selective pressure for larger plates. On the other hand, 0. gray ii may well be exposed to abrasion because of the nook and cranny feeding behavior of sea snakes, and this would argue for selection pressure in the other direction. Octolasmis weberi and 0. orthogonia with intermediate levels of plate coverage (34.8% and 41.5%, respectively) (Fig. 4) live on the exposed surface of horny corals and may derive safety from predation because of the nematocysts of the corals, and protection from abrasion because of the sedentary habit of the corals. Octolasmis carpilii is another species with low plate coverage (14.8%) that lives on the external surface of its host, but it has been found only on the base of the cheliped of a decapod, a site of considerable protection from both predation and abrasion. Octolasmis aymonini (18.2% plate coverage of the capitulum), 0. dawsoni (from isopod pleopods; 25.9% coverage), 0. geryonophila (27.7%), 0. hawaiense (53.1 %), and 0. indubia (on mouthparts of Scyllarides squamosus (Milne- VORIS I 7 . . ‘. AND JEFFRIES: CAPITULAR Edwards): 59.7% coverage) are from hosts that came from deep water (>300 m) well below the photic zone. We surmise that deep water affords safety from many visual predators, but may afford little or no protection from abrasion in cases where the barnacle is located on the mouthparts of the host. Thus, many of the species that do not clearly fall into the first two categories of exposure-plate relationship (more exposure/ more plate coverage versus less exposure/less plate coverage) may, in fact, be protected or sheltered by some other means. Other factors, of which we have only a rudimentary understanding, may also have confounding effects on establishing simple relationships. For example, species of Octolasmis living within gill chambers and protected from predation and abrasion may nonetheless be subjected to considerable current turbulence, thus requiring more support and hence more plate coverage. Only further detailed research can resolve the importance of these and other, presently unrecognized, special circumstances. At this point it is important to recognize some of the limitations that affect this study. First, the sample of species of Octolusmis and the specimens chosen to represent them were not random or exhaustive, but largely dependent on availability. Second, the methods of measurement employed were limiting. The lateral surface of the capitulum of Octolusmis is generally convex, not flat. The convexity is pronounced near the carinal margin where the single carina is located, and thus small differences in the viewing plane can generate large differences in the amount of the carina in view and hence the measurement of its area. This source of variation due to technique alone should be eliminated in future work, because it likely obscures more subtle sources of individual variation that may be’ biologically interesting. Nonetheless, we have moved beyond speculation regarding the relationships among the functions and variability in plate coverage of the capitula of Octolasmis, to a quantified data base on which to direct and build future research. It should also be noted that the quantitative investigation of variation in plate size and capitulum coverage has important implications for future studies of taxonomy of a variety of pedunculate cirripedes, where capitular plate information has been used in the past (Newman, 1967; Newman et al., 1967). PLATES 225 IN OCTOLdSMIS ACKNOWLEDGEMENTS / We thank the National University of Singapore (NUS) and the Phuket Marine Biological Center (PMBC) for their logistical support and for the use of their facilities over several years, In particular, we are grateful to Mrs. Yang Chang Man, Miss Lua Hui Kheng, Mr. Keng Loo Yeo, Mrs. Simon Greasi, and Mr. Kelvin Lim for assistance and support at the Zoological Reference Collection at NUS. At the PMBC we owe special thanks to Mr. Sombat Poovachiranon, Mr. Boonchoy Kuoyratanakul, a fisherman who collected most of the crabs, and Mr. Saengdee Chailert who received crabs from fishermen for us. We also appreciate the skilled assistance of numerous Dickinson College students, especially Amy Hewitt, Keow Thavaradhara, Peter Lovell, and Melinda Anderman. Support from the Dickinson College Faculty Research Fund and the Field Museum of Natural History made this investigation possible. We greatly appreciate the extensive comments on the manuscript by Helen Voris. We thank the following colleagues for the loan of specimens from their respective institutions: Danielle Defaye, Museum National d’Histoire Naturelle, Paris; Diana Jones, Western Australia Museum, Perth; Dietmar Keyser, Zoologisches Institut und Zoologisches Museum, Der Universitiit Hamburg, Hamburg; Eric Lazo-Wasem, Division of Invertebrate Zoology, Peabody Museum of Natural History, New Haven, Connecticut; Karen Reed, Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C.; Gary Rosenberg, Academy of Natural Sciences of Philadelphia, Philadelphia, Pennsylvania; John W. Short, Cmstacea Section, Queensland Museum, South Brisbane, Queensland, Australia; Karin Sindemark, Department of Invertebrate Zoology, Swedish Museum of Natural History, Stockholm; and Shigeyuki Yamato, Seto Marine Biological Laboratory, Kyoto University, Shirahana, Nishimuro, Wakayama, Japan. LITERATURE CITED Anderson, D. T. 1994. Barnacles: structure, function, development and evolution.-Chapman and Hall, London, England. Pp. l-357. Annandale, N. 1909. An account of the Indian Cirripedia Pedunculata. Part I. Family Lepadidae (sensu stricto).Memoirs of the Indian Museum 2: 59-137. Aurivillius, C. W. S. 1892. Neue Cirripeden aus dem Atlantischen, Indischen und Stillen Ocean.-Gfversigt af Kungliga Vetenskaps-Akademiens Fbrhandlingar 3: 123-134. -. 1894. Studien iiber Cirripeden-Kungliga Svenska Vetenskaps-Akademiens Handlinger 26 (7): l-107. Causey, D. 1960, Octolasmis dawsoni, new species (Cirripedia:Lepadidae) from Bathynomus giganteus.-Proceedings of the Biological Society of Washington 73: 93-98. Chemyshev, B. I. 1931. Cirripedien aus dem Bassin des Donez und von Kusnetxk.-Zoologischer Anzeiger 92: 26-28. Coker, R. E. 1902. Notes on a species of barnacle (Dichelaspis) parasitic on the gills of edible crabs.- 226 JOURNAL OF CRUSTACEAN BIOLOGY, Bulletin of the United States Fish Commission 21: 401-411. Darwin, C. 1851. A monograph on the sub-class Cirripedia. I. The Lepadidae.-Ray Society, London, England. Pp. l-400. -. 1854. A monograph on the the sub-class Cirripedia. The Balanidae: the Verrucidae, etc.-Ray Society, London, England. Pp. l-684. Foster, B. A. 1987. Barnacle ecology and adaptation.In: A. J. Southward, ed., Crustacean issues 5, Barnacle biology. Pp. 113-133. A. A. Balkema, Rotterdam, The Netherlands. Gray, J. E. 1825. A synopsis of the genera of cirripedes arranged in natural families, with a description of some new species.-Annals of Philosophy 10: 97-107. Hiro, F. 1936. Descriptions of three new species of Cirripedia from Japan.-Bulletin of the Biogeographical Society of Japan 6: 221-230. -. 1939. Studies on the cirripedian fauna of Japan. III. Supplementary notes on the cirripeds found in the vicinity of Seto.-Memoirs of the College of Science, Kyoto Imperial University Series B 15: 237-244. Hoek, P. P C. 1907. The Cirripedia of the Siboga-Expedition. A. Pedunculam-Siboga Expeditie Monographe 31a. Pp. 1-127. E. J. Brill, Leiden, The Netherlands. Jeffries, W. B., and H. K. Voris. 1983. The distribution, size, and reproduction of the pedunculate barnacle, Octolasmis miilleri (Coker, 1902), on the blue crab, Callinectes sapidus (Rathbun, 1896).-Fieldiana, Zoology (new series) 16: l-10. -, and -. (In press.). A subject-indexed bibliography of Octolasmis.-Raffles Bulletin of Zoology. -, -, and C. M. Yang. 1982. Diversity and distribution of the pedunculate barnacle Octolasmis in the seas adjacent to Singapore.-Journal of Crustacean Biology 2: 562-569. -, and -. 1984. Diversity and distri-, bution of the pedunculate barnacle Octolasmis Gray, 1825, epizoic on the scyllarid lobster, Thenus orientalis (Lund, 1793).-Crustaceans 46: 300-308. -,and-. 1988. Octolasmis collare, a new &ecies of pedunculate barnacle from the seas adjacent to Singapore.-Indo-Malayan Zoology 5: 11 l-l 16. -, and -. 1989. Observations on the -1 incidence of the pedunculate barnacle, Octdlasmis warwickii (Gray, 1825) on horseshoe crabs (Xiphosura) in the seas adjacent to Singapore.-Raffles Bulletin of Zoology 37: 58-62. -, and -. 1991. Species recognition among the pedunculate barnacles (Cirripedia: Thoracica) on the mangrove crab, Scylla serrata.-Raffles Bulletin of Zoology 40: 83-92. Lessona, C., and C. Tapparone-Canefri. 1874. Nota sulla Macrocheira kaempferi Sieb. e sopra una nuova sp. de1 gen. Dichelaspis.-Atti della Accademia delle Scienze di Torino 9: 185-194. MacDonald, J. 1869. On an apparently new genus of minute parasitic cirriped, between Lqas and Dichelapsis.-Proceedings of the Zoological Society of London. 1869. Pp. 440-444. Newman, W. A. 1960. Octolasmis californiana, spec. VOL. 17, NO. 2, 1997 nov., a pedunculate barnacle from the gills of the California spiny lobster.-Veliger 3: 9-l 1. _--. 1961. OIJ certain littoral speciesof Octolasmis (Cirripedia, Thoracica) symbiotic with decapod Crustacea from Australia, Hawaii, and Japan.-Veliger 4: 99-107. -. 1967. Shallow-water versus deep-sea Octolasmis (Cirripedia Thoracica).-Crustaceana 12: 13-32. -. 1987. Evolution of cirripedes and their major groups.-Zn: A. J. Southward, ed., Crustacean issues 5, Barnacle biology. Pp. 3-42. A. A. Balkema, Rotterdam, The Netherlands. -, V. A. Zullo, and S. A. Wainwright. 1967. A critique on recent concepts of growth in Balanomorpha (Cirripedia, Thoracica).-Crustaceana 12: 167-178. Nilsson-Cantell, C. A. 1921. Cirripeden Studien. Zur Kenntnis der Biologie, Anatomie und Systematik dieser Gruppe.-Zoologiska Bidrag f&t Uppsala 7: 75-390. Pearse, A. S. 1947. On the occurrence of ectoconsortes on marine animals at Beaufort, N.C.-Journal of Parasitology 33: 453-458. Pilsbry, H. A. 1907. The barnacles (Cirripedia) contained in the collection of the U.S. National Museum Smithsonian Institution.-United States National Museum Bulletin 60: 1-122. -. 1916. The sessile barnacles (Cirripedia) contained in the collections of the U.S. National Museum; including a monograph of the American species.United States National Museum Bulletin 93: l-366. Rose&N. C. 1967. The Philippine Cirripedian fauna: I. Some pedunculate cirripeds from Iloilo waters and adjacent seas.-Natural and Applied Science Bulletin 20: 277-3 19. S&ram, F. 1982. The fossil record and evolution of Crustacea.-Zn: D. E. Bliss, ed.-in-chief, The biology of Crustacea. Vol. 1. L. G. Abele, ed., Systematics, the fossil record, and biogeography. Pp. 93-147. Academic Press, New York, New York. Stebbing, T. R. R. 1895. Notes on Crustacea. Two new pedunculate Cirripedia.-Annals and Magazine of Natural History (6) 15: 18-25. Wells, H. W. 1966. Barnacles of the northeastern Gulf of Mexico.-Quarterly Journal of the Florida Academy of Sciences 29: 81-95. Wills, L. J. 1963. Cyprilepas holmi Wills 1962, a pedunculate cirripede from the Upper Silurian of Oesel, Esthonia.-Paleontology 6: 161-165. Zevina, G. B. 1982. Barnacles of the suborder Lepadomorpha (Cirripedia, Thoracica) of the world ocean.Part 2: Guides to the Fauna of the USSR 133. Pp. l-222. Zoological Institute, Academy of Sciences of the USSR, Leningrad, Russia. [In Russian.] Zullo, V. A. 1982. Cirripedia.-Zn: S. P Parker, ed., Synopsis and classification of living organisms. Pp. 220-232. McGraw-Hill, New York, New York. RECEIVED: ACCEPTED: 8 June 1996. 8 October 1996. Addresses: (HKV) Department of Zoology, Field Museum of Natural History, Chicago, Illinois 60605, U.S.A.; (WBJ) Department of Biology, Dickinson College, Carlisle, Pennsylvania 17013, U.S.A. (e-mail:voris@ fmppr.fmnh.org)