YAMAGUTICESTUS LONGICOLLIS (MOLIN, 1858)

Caira, Janine N., Bueno, Veronica & Jensen, Kirsten, 2021, Emerging global novelty in phyllobothriidean tapeworms (Cestoda: Phyllobothriidea) from sharks and skates (Elasmobranchii), Zoological Journal of the Linnean Society 193, pp. 1336-1363 : 1350

YAMAGUTICESTUS LONGICOLLIS (MOLIN, 1858) COMB. NOV.

BASIONYM: TETRABOTHRIUM LONGICOLLIS MOLIN, 1858, AS ‘ LONGICOLLE ’

A detailed account of the taxonomic history of Y. longicollis was provided by Ruhnke (2011) in his monograph on the Phyllobothriidae . Given the lack of figures and the brevity of the original description by Molin (1858), Ruhnke (2011) discussed the redescription and associated specimens of Euzet (1959) from the type host, Scyliorhinus stellaris (Linnaeus, 1758) , and included photomicrographs of one of Euzet’s specimens (MNHN HEL 138). In that work, Ruhnke (2011) treated this species as incertae sedis under the name Crossobothrium longicolle (Molin, 1858) Euzet, 1959 , noting that, although it failed to conform to the diagnosis of Crossobothrium and in fact resembled P. squali , a more appropriate generic home was unavailable at that time. This species as redescribed by Euzet (1959) and characterized by Ruhnke (2011) is fully consistent with the concept of Yamaguticestus advanced here. We hereby transfer this species to the new genus as Yamaguticestus longicollis . It differs conspicuously from Y. squali in its possession of a smaller scolex that is much longer than wide (600–800 by 300–400 vs. 2900 in diameter).

Our results help to resolve a puzzling issue surrounding the identity of a specimen collected from the catshark Scyliorhinus canicula off the UK, for which sequence data for the D1–D3 region of the 28S rDNA gene ( AF286958 ; LRP no. 2113) were generated by Olson et al. (2001). These authors referred to this specimen as Crossobothrium longicolle . However, Ruhnke & Workman (2013) found this specimen to be morphologically consistent with, and identical in sequence to, a specimen they identified as Phyllobothrium squali ( KC543441 ; LRP no. 7967) collected from the dogfish Squalus acanthias off Rhode Island. In the absence of reports of Y. squali or any of its relatives from catsharks, Ruhnke & Workman (2013) suggested that this cestode and the host from which it came might have been misidentified by Olson et al. (2001). In the tree resulting from our analysis, Olson et al. ’s (2001) specimen of ‘ Crossobothrium longicolle ’ groups robustly among species of Yamaguticestus , members of which we now know can be hosted by either squaliform sharks or catsharks. This suggests that the original identification of the host of this specimen as Scyliorhinus canicula was probably correct. However, the specific identity of this specimen as ‘ C. longicolle ’ is doubtful given that the type host of Y. longicollis is Scyliorhinus stellaris . The fact that the sequences are identical is insufficient to reject this hypothesis given the low amount of sequence divergence seen among members of this genus in this region of the 28S rDNA gene. As a consequence, we believe this species is likely to represent an undescribed member of the genus, the description of which will require examination of additional material.