Plagiorchiida, La Rue, 1957

Katahira, Hirotaka, Shirakawa, Hokuto & Nagasawa, Kazuya, 2014, Five Trophically-transmitted Parasites from Adult Arctic Lampreys Lethenteron camtschaticum (Petromyzontiformes: Petromyzontidae): Biological Indicators of the Host’s Marine Life as a Predator, Species Diversity 19, pp. 157-165 : 159

( Plagiorchiida : Lecithasteridae ) ( Fig. 1B )

Description. One mature specimen (NSMT–Pl 6136) examined. Trunk 2,250 long, its maximum width 810, with small papillae on posterior end. Oral sucker 150× 178 in length and width. Ventral sucker 288× 270 in length and width. Pharynx 120× 92.5 in length and width. Oesophagus short, 100 long. Intestinal caeca blind. Excretory arms obscure due to poor staining. Genital pore opening medially between oral sucker and ventral sucker. Terminal genitalia with reduced genital atrium, no permanent sinus organ and oval sinus-sac. Pars prostatica well developed. Seminal vesicle globular. Testes ovoid; left one 185×143; right one 175×130. Ovary with four lobes, 110–125 (117.5) in maximum diameter; seminal receptacle antero-dorsal to ovary. Vitellarium with seven tear-shaped lobes, with individual lobe 80–125 (96.4) in maximum diameter. Uterus extending from level of ventral sucker to posterior end of body. Eggs oval, 22–23 (22.5)×15–17 (15.9) in length and width (n =10; measurements taken through body wall of mounted specimen).

Remarks. The single specimen has larger eggs than usual for a member of the genus Lecithaster Lühe, 1901 (see Srivastava 1966). Lecithaster confusus Odhner, 1905 is closely similar to this specimen but has smaller eggs (15– 17×7 µm) ( Odhner 1905). Lecithaster stellatus Looss, 1907 also resembles our specimen but differs in having smaller eggs (15–17×9–11 µm) and narrower vitelline lobes ( Looss 1908). Only L. gibbosus agrees with our specimen in characters such as egg size, the presence of the ventral sucker about twice as large as the oral sucker, and the seminal vesicle located postero-dorsal to the ventral sucker ( Srivastava 1966; Gibson 1996).

Lecithaster gibbosus is known to use snails of the pyramidellid genus Odostomia Fleming, 1813 and the muricid genus Thais Röding, 1798 as first intermediate hosts ( Ching 1960; KØie 1989) and planktonic copepods of the genera Acartia Dana, 1846 , Centropages KrØyer, 1849 , and Pseudocalanus Boeck, 1872 as second intermediate hosts ( Boyce 1969; KØie 1989). The definitive hosts are various marine fishes, including clupeids, salmonids, gadids, and pleuronectids (e.g., Love and Moser 1983; Arai 1969), occurring in Arctic and boreal waters of the North Atlantic and North Pacific (see Gibson 1996). Oncorhynchus spp. and Stichaeus grigorjewi are known to harbour this digenean in waters around Hokkaido ( Machida et al. 1972; Nagasawa et al. 1987).

Figures

Fig. 1. Endoparasites from adult Arctic lampreys Lethenteron camtschaticum (Tilesius, 1811) from the Ishikari River, Hokkaido. A, Brachyphallus crenatus (Rudolphi, 1802); B, Lecithaster gibbosus (Rudolphi, 1802); C, Nybelinia surmenicola (Okada in Dollfus, 1929); D, metabasal armature of a tentacle of N. surmenicola; E, tetraphyllidean plerocercoid; F, male specimen of Bolbosoma sp.; G, female specimen of Bolbosoma sp. Scale bars: A–B, 500µm; C, E–G, 2mm; D, 50µm.