Tetraphyllidea, Carus, 1843

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 : 161

( Tetraphyllidea : Phyllobothriidae ) ( Fig. 1E )

Description. Ten plerocercoids (NSMT–Pl 6139, 6140) examined. Whole body, consisting of scolex, neck and tail, 1,900 –6,875 (5,133) long and 740–1,470 (1,058) wide at about midlength. Scolex with four bothridia, maximum width in region of scolex 880–2,250 (1,684). Bothridia 330–815 (673)×315–620 (520) in length and width, with four anterior accessory suckers 160–285 (252)×165–310 (263) in length and width. Apical sucker round, 125–250 (212)×165–260 (227) in length and width. Neck short, 680– 1,400 (1,023) wide.

Remarks. This type of larvae is commonly known as Scolex pleuronectis Müller, 1780, belonging to the order Tetraphyllidea Carus, 1843 ( Euzet 1994) . Our specimens can be further specified as phyllobothriid larvae in view of their tail and apical sucker ( Scholz et al. 1998). One of the candidate species is Pelichnibothrium speciosum Monticelli, 1889 , as its plerocercoids have been reported from the loliginid squid Loligo sp. and the chum salmon Oncorhynchus keta (Walbaum, 1792) in Japanese waters ( Yamaguti 1934). If our specimens retain their larval features in the definitive hosts ( Scholz et al. 1998), they could be P. speciosum . Incidentally, Phyllobothrium caudatum (Zschokke and Heitz, 1914) and Phyllobothrium salmonis Fujita, 1922 , previously found in various salmonids off Japan ( Fujita 1922; Margolis 1957; Zhukov 1960; Urawa 1989; Awakura 1994) are other candidates, but they are all suspected synonyms of P. speciosum ( Yamaguti 1934; Nagasawa et al. 1987; but see Williams 1968).

Shimazu (1975a) reported similar plerocercoids, presumably identical to P. speciosum , in euphausiid crustaceans from the northern North Pacific. This species is thought to complete its life-cycle in the blue shark Prionace glauca (Linnaeus, 1758) ( Yamaguti 1934; Scholz et al. 1998) through the ingestion of fish second intermediate hosts, such as salmonids, and cetacean paratenic hosts.

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.