Mesobathylebouria, Martin & Huston & Cutmore & Cribb, 2019

MESOBATHYLEBOURIA View in CoL GEN. NOV.

Diagnosis: Body oval to elongate-oval, dorso-ventrally flattened. Forebody about one-quarter to one-third body length. Tegument smooth, relatively thick. Oral sucker unspecialized, terminal or subterminal. Ventral sucker unspecialized, larger than oral sucker. Prepharynx short. Pharynx unspecialized, smaller than oral sucker. Oesophagus unspecialized. Intestine bifurcates in forebody. Caeca blind, extending near to posterior extremity. Testes two, smooth or irregularly lobed, medial, usually contiguous; post-tesicular zone about one-tenth to over one-quarter body length. Cirrus-sac well developed, short, claviform, not extending into hindbody. Seminal vesicle internal, broad. Pars prostatica present. Ejaculatory duct relatively long. Common genital atrium short, simple. Genital pore pre-bifurcal, sinistro-submedial. Ovary irregularly lobed, medial to dextro-submedial, anterior to and contiguous with anterior testis, separated from ventral sucker. Seminal receptacle canalicular, smaller than ovary. Laurer’s canal present, short, opens dorsal to ovarian complex. Mehlis’ gland present. Uterus preovarian, usually intercaecal. Vitellarium follicular, dense, extending from near to posterior extremity to level of intestine bifurcation or beyond, may be interrupted at level of ventral sucker, may become confluent in post-testiuclar zone or forebody. Eggs oval, operculate, unembryonated in utero, <80 µm long. Excretory vesicle tubular, extends to level of ovary.

In Indo-West Pacific marine fishes of several orders, mainly from the mesopelagic zone.

Ty p e - s p e c i e s: M e s o b a t h y l e b o u r i a l a n c e o l a t a (Price, 1934) comb. nov. [syn. Podocotyle lanceolata , Neolebouria lanceolata (Price, 1934) Reimer, 1987 ].

Other species: Mesobathylebouria acanthogobii (Yamaguti, 1951) comb. nov. [syn. Plagioporus acanthogobii , Neolebouria acanthogobii (Yamaguti, 1951) Gibson, 1976 ]; M. lobata (Yamaguti, 1934) comb. nov. [syn. Lebouria lobata , Neolebouria lobata (Yamaguti, 1934) Gibson, 1976 ]; M. tinkerbellae (Thompson & Margolis, 1987) comb. nov. (syn. Neolebouria tinkerbellae ); M. tohei (Yamaguti, 1970) comb. nov. [syn. Plagioporus tohei , Neolebouria tohei (Yamaguti, 1970) Gibson, 1976 ].

ZooBank registration LSID: http://www.zoobank. org/ urn:lsid:zoobank.org:act:9752A24C-CBFD-48F9-AEA3-A349CDBAE7F4

Etymology: The generic name is composed from Greek meso, middle, and bathos, deep, combined with the genus Lebouria Nicoll, 1909 , named after Dr Marie Lebour and the stem for Neolebouria , but now a junior synonym of Peracreadium Nicoll, 1909 . The name is chosen because these species are morphologically similar to those of Neolebouria and are generally found in fishes from the lower epipelagic to mesopelagic zone. The genus is to be treated as feminine.

Remarks: Neolebouria currently comprises 11 species [plus N. maorum (Allison, 1966) Gibson, 1976 incertae sedis], but these must be considered to represent at least two genera because N. georgiensis Gibson, 1976 , the type-species, and N. lanceolata do not resolve together in molecular phylogenetic analyses ( Faltýnková et al., 2017; Martin et al., 2017). Neolebouria georgiensis is almost certainly congeneric with N. antarctica (Szidat & Graefe, 1967) Zdzitowiecki, 1990 and N. terranovaensis Zdzitowiecki et al., 1993 . These three species are known only from Antarctic and sub-Antarctic waters, in notothenioid perciform fishes (Artedraconidae, Bathydraconidae , Channichthyidae and Nototheniidae ) and also species of Paraliparis ( Scorpaeniformes : Liparidae ) ( Gibson, 1976; Zdzitowiecki, 1987, 1991, 1997; Zdzitowiecki et al., 1993; Palm et al., 2007). As per Martin et al. (2017), we consider one other nominal species, Neolebouria merretti Gibson & Bray, 1982 , to be more convincingly congeneric with N. georgiensis than N. lanceolata . It is known from an ipnopid ( Aulopiformes ) collected at 2985–3311 m deep south-west of the Canary Islands ( Gibson & Bray, 1982). These four species have large (1800–4800 µm long), robust bodies, thick tegument, medial and irregularly lobed gonads and large eggs, greater than 80 µm long. In N. georgiensis , N. merretti and N. terranovaensis the cirrus-sac reaches to about the level of the posterior margin of the ventral sucker or a little beyond into the hindbody, although in N. antarctica it is much shorter. The original descriptions for N. georgiensis and N. merretti are highly detailed ( Gibson, 1976; Gibson & Bray, 1982) and thus two potentially significant characters serve to convincingly unite these species. First, in each species, the entirety of the oesophagus, and also the anterior part of the caeca in N. merretti , is surrounded by especially dense gland cells, and second, the seminal vesicle is broad and dilate proximally but then becomes long, thin, coiled and duct-like prior to the pars-prostatica and ejaculatory duct.

We propose Mesobathylebouria for N. lanceolata and four of the remaining six species of Neolebouria : N. acanthogobii , N. lobata , N. tinkerbellae and N. tohei . Collectively, these five species occur in a broad range of fishes from mainly the lower epipelagic to mesopelagic zone, but not including notothenioids, other Antarctic/ sub-Antarctic fishes or indeed other perciform fishes: Anguilliformes ( Nettastomatidae , Congridae ), Aulopiformes ( Ipnopidae ), Lophiformes ( Chaunacidae ), Ophidiiformes ( Ophidiidae ), Polymixiiformes ( Polymixiidae ), Scorpaeniformes ( Hoplichthyidae , Triglidae ) and Stomiiformes (Phosicthyidae) (Martin et al., 2017 and references therein). Four of these species have Indo-Pacific distributions, N. acanthogobii and N. lobata are both known from off Japan and Mozambique, N. tohei is known from Hawaii and N. tinkerbellae is known from off British Columbia, whereas N. lanceolata is known from the Gulf of Mexico and the Caribbean and also from off Mozambique. Species included here in Mesobathylebouria can be distinguished most objectively from those retained in Neolebouria (s.s.) by smaller eggs, measuring less than 80 µm long. These species are also less robust and some have a dextro-submedial ovary or smooth testes. In N. lanceolata the cirrus-sac almost reaches to the posterior margin of the ventral sucker, but in the other four species it is either entirely anterior to the ventral sucker or overlaps only the anterior portion.

Two nominal Neolebouria species are unaccounted for, N. leiognathi ( Wang et al., 1992) Bray, 2002 and N. pentacerotis Machida & Araki, 2002 . Neolebouria leiognathi is known from the deep pugnose ponyfish Secutor ruconius ( Perciformes : Leiognathidae ), a small coastal fish, off China ( Wang et al., 1992). It has almost equal suckers, a neatly trilobed ovary, eggs greater than 90 µm long and possibly a medial genital pore. It is unlikely to belong in either Neolebouria or Mesobathylebouria , but its placement elsewhere is difficult. Few opecoelids are known from leiognathids and none bear particular resemblance to N. leiognathi . The original description is lacking in detail and thus, for the present, we consider N. leiognathi a species incertae sedis. Neolebouria pentacerotis is known from the Japanese armourhead Pentaceros japonica ( Perciformes : Pentacerotidae ), a lower epipelagic to mesopelagic fish, collected at depth in Japanese waters ( Machida & Araki, 2002). It has exceptionally small eggs, 27–33 µm long, and thus is consistent with the concept of Choerodonicola Cribb, 2005 , species of which are known only from perciform fishes, including in Japanese waters. Choerodonicola may be polyphyletic ( Martin et al., 2018a), based on sequence data available for two species: one, C. arothokoros Martin et al., 2018 , in which the ovary is entire and the other, C. renko Machida, 2014 , in which it is lobed. In the type-species, C. choerodontis (Yamaguti, 1934) Cribb, 2005 , the ovary has an intermediate, irregularly lobed condition. Of the two sequenced representative species, N. pentacerotis is probably more closely related to C. renko Machida, 2014 , which is known from two Japanese sparids: the yellowfin seabream Dentex abei Iwatsuki et al. and the yellowback seabream D. hypselosomus Bleeker , which reportedly range from depths of 50 to 200 m ( Iwatsuki et al., 2007). Thus, we propose Choerodonicola pentacerotis ( Machida & Araki, 2002) comb. nov. It is distinguishable within the genus by a distinct interruption in the vitelline field at the level of the ventral sucker; C. interruptus (Manter, 1954) Martin et al., 2018 also has an interrupted vitelline field, but the interruption is at the level of the testes in that species and it is known only from a labrid ( Perciformes ) endemic to New Zealand.