Bathypodocotyle, Martin & Huston & Cutmore & Cribb, 2019

BATHYPODOCOTYLE View in CoL GEN. NOV.

Diagnosis: Body elongate-oval, dorso-ventrally flattened, large. Tegument smooth. Oral sucker, unspecialized, terminal or subterminal. Ventral sucker unspecialized, larger than oral sucker, may be protuberant. Prepharynx short. Pharynx unspecialized, slightly smaller than oral sucker. Oesophagus unspecialized. Intestine bifurcates in forebody. Caeca blind, extending beyond testes near to posterior extremity. Testes two, smooth, round or wedge shaped, medial, contiguous; post-tetsicular zone occupies at least one-quarter total body length. Cirrus-sac well developed, short, retrorse oval, restricted to forebody or overlapping anterior portin of ventral sucker. Seminal vesicle internal, occupying most of cirrus-sac, sinuous, broad proximally, becoming long, sinuous and narrow, almost duct-like, distally. Pars prostatica prominent. Ejaculatory duct exceptionally short. Common genital atrium simple. Genital pore pre-bifurcal, sinistro-submedial. Ovary smooth, medial or dextro-submedial, contiguous with anterior testis. Seminal receptacle canalicular, smaller than ovary, retrorse. Laurer’s canal present, opens dorsal to ovary. Mehlis’ gland present. Uterus preovarian, intercaecal. Vitellarium follicular, dense, restricted to hindbody, becoming confluent in post-testiuclar zone, extending near to posterior extremity. Eggs oval, operculate, unembryonated in utero. Excretory vesicle tubular, extends to level of ovary. Excretory pore terminal. In mesopelagic and bathypelagic north Atlantic and north Pacific fishes of the Macrouridae ( Gadiformes ).

Type-species: Bathypodocotyle margolisi ( Gibson, 1995) comb. nov. (syn. Allopodocotyle margolisi ).

Other species: Bathypodocotyle enkaimushi (Blend et al., 2015) comb. nov. (syn. Allopodocotyle enkaimushi ).

ZooBank registration LSID: http://www.zoobank. org/ urn:lsid:zoobank.org:act:097A860F-3892-413A-805E-790D00548435

Etymology: The generic name is composed from Greek bathos, deep and the existing opecoelid genus Podocotyle , itself from podo-, relating to the foot and kotyle, a cup. The name is chosen because the new genus is comprised of deep-sea taxa previously recognized in Allopodocotyle , which itself is based on similarity to the concept of Podocotyle .

Remarks: Allopodocotyle is loosely defined, accommodates many species and is evidently polyphyletic. The genus currently comprises about 24 species from a broad range of marine fishes, united, among typically ‘plagioporine’ genera, by an entire ovary and restriction of the vitelline follicles to the hindbody ( Cribb, 2005). The type-species, A. plectropomi (Manter, 1963) , Pritchard, 1966, and its most convincing congeners, are known from Indo-West Pacific groupers ( Perciformes : Serranidae : Epinephelinae). Sequence data have been published, by Bray et al. (2016), for four species considered to belong in Allopodotyle: A. epinepheli (Yamaguti, 1942) Pritchard, 1966 , A. margolisi and two species identified only to genus. Data for A. epinepheli and one of the unidentified species, both collected from Indo-West Pacific groupers, resolve together in the large marine Plagioporinae (s.l.) clade. We consider these data to represent the phylogenetic position of genuine Allopodocotyle species. Allopodocotyle margolisi is phylogenetically distant from these taxa and is known from the Mediterranean grenadier Coryphaenoides mediterraneus (Giglioli) ( Gadiformes : Macrouridae ), collected at 1745–2195 m deep from the Rockall Trough in the north-east Atlantic ( Gibson, 1995). Compared with A. epinepheli , A. plectropomi and also A. serrani (Yamaguti, 1952) Pritchard, 1966 , another convincing species known from Indo-West Pacific groupers, A. margolisi is most distinguishable by the configuration of its terminal genitalia. It has a short cirrus-sac not extending into the hindbody and an exceptionally short ejaculatory duct vs. a relatively long cirrus-sac extending well into the hindbody with a long ejaculatory duct occupying at least half the length of the cirrus-sac. Allopodocotyle margolisi can further be distinguished from these species in that it has medial and contiguous vs. diagonal and separate testes and in that the vitelline follicles extend anteriorly to the posterior margin of the ventral sucker vs. only to the level of the ovary or a little beyond. One other nominal species of Allopodocotyle agrees more closely in its morphology and ecology with A. margolisi than with species from Indo-West Pacific groupers: A. enkaimushi has an exceptionally short ejaculatory duct and cirrus-sac, medial and contiguous testes, and vitelline follicles restricted to the hindbody but extending anteriorly to the posterior margin of the ventral sucker. It is also known from macrourids, collected at depths between 681 and 1061 m off Japan (Blend et al., 2015). We propose Bathypodocotyle for these two species. We think that these species are probably closely related to other taxa known from deep-sea macrourid fishes, specifically species of Macrourimegatrema , Tellervotrema and some species of Podocotyle , as well as species of Neolebouria (s.s). However, none of these concepts can adequately accommodate the taxa included here in the new genus: Macrourimegatrema is defined for species with a funnel-shaped oral sucker and a more elongate body, species of Tellervotrema and Podocotyle have lobed ovaries, and species of Tellervotrema and Neolebouria have vitelline follicles entering the forebody.