Buticulotrema thermichthysi, Bray, R. A., Waeschenbach, A., Dyal, P., Littlewood, D. T. J. & Morand, S., 2014

Bray, R. A., Waeschenbach, A., Dyal, P., Littlewood, D. T. J. & Morand, S., 2014, New digeneans (Opecoelidae) from hydrothermal vent fishes in the south eastern Pacific Ocean, including one new genus and five new species, Zootaxa 3768 (1), pp. 73-87 : 82-84

Buticulotrema thermichthysi n. sp.

( Figs. 8–9 )

urn:lsid:zoobank.org:act:F1BC29FC-883D-4A62-92CC-C54B6880E039

Type host. Thermichthys hollisi (Cohen, Rosenblatt & Moser) (Ophididiiformes: Bythitidae ), Hollis brosmekvabbe.

Site. Large intestine

Type locality. South East Pacific Rise, hydrothermal vent site Hobbs, 17°35.20’S, 113°14.75’W; Biospeedo cruise, PL 1588, depth 2598 m, baited trap, 29 Apr. Biospeedo labels: 1588–3, 1588–7.

Type specimens. MNHM holotype 1 slide MNHN HEL 405, paratypes 3 wholemount slides MNHN HEL 406 407, 6 section slides MNHN HEL 409 410 411 412 413 414; BMNH paratypes 2013.12.3.11-13.

GenBank numbers. rDNA KF733984 , rDNA KF733987

Possible juvenile. Ventichthys biospeedoi , South East Pacific Rise, hydrothermal vent site Oasis, 17°25.38’S, 113°12.29’W; Biospeedo cruise, submersible Nautile, R/V Atalante, dive PL 1582, baited trap B2, depth 2586 m, 22 April 2004. Biospeedo label: 1582–2 (juv.), MNHN HEL 408.

Etymology. This species is named after the host-genus.

Description. Based on 8 wholemounts and 4 sets of serial sections. Measurements and ratios in Table 1. Body elongate pyriform, widest in anterior hindbody ( Fig. 8 ). Tegument unarmed. Oral sucker subglobular, subterminal. Ventral sucker rounded, larger than oral sucker, just pre-equatorial. Prepharynx dorsal to oral sucker. Pharynx subglobular, large. Oesophagus long, very thick-walled. Intestinal bifurcation dorsal to posterior part of ventral sucker. Caeca blind, narrow, reaching well into post-testicular region, but not to posterior extremity.

Testes irregularly oval or pyriform, oblique, contiguous, in mid-hindbody. Cirrus sac absent. Seminal vesicle saccular, in anterior hindbody and overlapping ventral sucker, narrow distally to form coiled tube ( Figs. 9 ). Pars prostatica long, with distinct field of gland-cells and fibrous tissue which may appear to be delimited in some views. Naked distal male duct (ejaculatory duct?) long, wall thickens slightly distally, no evidence of cirrus sac or everted cirrus. Genital atrium subglobular. Genital pore sinistral, beside mid- to posterior part of pharynx.

Ovary oval to reniform, just anterior to dextral testis or more median. Female proximal system unclear, even in sections. Seminal receptacle saccular, presumably canalicular. Laurer’s canal not traced. Mehlis’ gland not clearly distinguished. Uterus pretesticular, intercaecal, passes to left of ventral sucker. Eggs large, operculate, tanned, numerous. Metraterm long, reaches from about mid-pars prostatica, fairly thin-walled. Vitellarium follicular, follicles large, field reaching from mid-pharynx to just into post-caecal region, not as far as posterior extremity, lateral and ventral to caeca, not confluent, although approaching in post-testicular zone.

Excretory pore terminal, in slight indentation. Vesicle I-shaped, surrounded by prominent gland-cells posterior, reaches to testes.

Remarks. The features distinguishing B. thermichthysi n. sp. from B. stenauchenus are the very long, very strongly muscular oesophagus, bifurcating dorsally to the posterior part of the ventral sucker, the long, narrow pars prostatica and distal male duct and the sinistral genital pore at the level of the pharynx.

It is possible that the female proximal system has been misinterpreted, and the organ considered by us to be a canalicular seminal receptacle is a uterine seminal receptacle. If that were the case then this species would be close to the genus Pseudopecoelus Von Wicklen, 1946 , a genus which has been frequently reported in deeper waters. None of the described species of Pseudopecoelus have a long, highly muscular oesophagus, reaching dorsally to the ventral sucker.

Figures

FIGURES 8 – 9. Buticulotrema thermichthysi n. sp. 8. Ventral view of holotype. 9. terminal genitalia. Abbreviations: C, caecum; E, Egg; ED, male duct - presumably ejaculatory duct; GP, genital pore; M, metraterm; Ov, ovary; PP, pars prostatica; SV, seminal vesicle; T, testis; U, uterus; V, vitelline follicle. Scale-bars: 8, 9, 200 µm.