Brachyphallus crenatus ( Rudolphi, 1802 )

Brachyphallus crenatus ( Rudolphi, 1802) View in CoL ( Plagiorchiida : Hemiuridae ) ( Fig. 1A View Fig )

Description. One mature specimen (NSMT–Pl 6135) examined. Trunk 2,550 long, with maximum width 550. Body surface plicate. Presomatic pit present anterior of ventral sucker. Ecsoma withdrawn, 300 long. Oral sucker 210× 245 in length and width. Ventral sucker 245× 250 in length and width. Pharynx 112.5× 110 in length and width. Oesophagus absent. Intestinal caeca blind. Genital pore opening medially between oral sucker and presomatic pit. Terminal genitalia with reduced genital atrium and no permanent sinus organ. Sinus-sac well developed. Pars prostatica surrounding anterior end of seminal vesicle. Seminal vesicle bipartite, with small anterior region and expanded posterior region. Testes ovoid, diagonal; anterior testis 148×220; posterior one 148×193. Ovary round, 200×210. Vitelline masses slightly lobate; right one with four lobes, 348×260; left one with three lobes, 295×200. Uterus restricted to area between ventral sucker and vitelline masses. Eggs elliptical, 25–27 (25.9)×11–13 (12.1) in length and width (n =10; measurements taken through body wall of mounted specimen).

Remarks. The present specimen belongs to the genus Brachyphallus Odhner, 1905 , based on the following characters: a bipartite seminal vesicle, the plicate body surface, a deep presomatic pit, and the presence of an ecsoma (see Gibson 2002a). Among the members of this genus, three species, viz., Brachyphallus brachygobii Reichenbach-Klinke, 1952 , Brachyphallus parvus ( Manter, 1947) , and B. crenatus , are similar to our specimen, but the first species has testes arranged in parallel and an unlobed vitellarium ( Reichenbach-Klinke 1952) and the second species has an atrophied ecsoma and a distinctly smaller body (525–1,215 µm vs 2,550 µm in our specimen) ( Manter 1947). The measurements and arrangements of the reproductive organs in the present specimen are consistent with those of B. crenatus .

KØie (1992) demonstrated the life-cycle of B. crenatus . She obtained its cercariae from the retusid snail Retusa obtusa (Montagu, 1803) and successfully infected the acartiid copepod Acartia (Acanthacartia) tonsa Dana, 1849 with them. Adult worms were recovered from three-spine sticklebacks Gasterosteus aculeatus Linnaeus, 1758 following feeding experiments with infected copepods. Brachyphallus crenatus occurs in various coastal marine fishes, especially clupeids, salmonids, gasterosteids, and pleuronectids, in the North Atlantic and North Pacific ( Gibson and Bray 1986; Gibson 1996). In Japanese waters, it has been reported from Osmerus dentex Steindachner and Kner, 1870 (Osmeridae) , Salvelinus leucomaenis leucomaenis (Pallas, 1814) and Oncorhynchus spp. (Salmonidae) , Sebastes itinus ( Jordan and Starks, 1904) and Sebastes oblongus Günther, 1877 (Sebasti- dae), Hemitripterus villosus (Pallas, 1814) (Hemitripteridae) , Stichaeus grigorjewi Herzenstein, 1890 and Stichaeus nozawae Jordan and Snyder, 1902 ( Stichaeidae ), and Hippoglossus stenolepis Schmidt, 1904 (Pleuronectidae) ( Machida et al. 1972; Nagasawa et al. 1989; Urawa and Kaeriyama 1999).