Pseudostichopus mollis Theel 1886

Pseudostichopus mollis Théel, 1886

(Figure 19)

Pseudostichopus mollis Théel, 1886:169 –170, pl. 10 figs. 5, 6; Branch et al. 1993: 55 (in key); O’Loughlin & Ahearn, 2005: 171 –173 (synonymy complete).

Pseudostichopus trachus Sluiter, 1901: 52 –53, pl. 5 fig. 1, pl. 8 fig 8.

? Pseudostichopus mollis Samyn & VandenSpiegel 2016:479, fig. 20.

Material examined. SAMC-A 090930, Marion Island, 46°44.5’ S– 45°44.5’ S, 37°40.9’ E– 37°37.4’ E, 909 m, 25. VI.2001, R. Leslie, 1 spec.

Diagnosis (see O’Loughlin & Ahearn 2005).

Description. Specimen well preserved (Figure 19A). Length about 127 mm, breadth in mid-body about 60 mm. Colour off-white, both dorsally and ventrally. Tentacles retracted, mouth ventral, anus terminal, anal furrow not distinct. Tube feet retracted, minute, easily overlooked in superficial study, scattered, scarcely 1 mm in length; suckers present/absent. Tentacles, including the ones removed in a previous study, about 16, with yellowish tips. Calcareous ring low, radial plates better developed than interradial plates and about twice as high; posterior margin of the ring undulating. Polian vesicle single, sac-like. Stone canal not observed. Gonad tubules (testis) may or may not be dichotomously branched distally. Respiratory trees well branched, right one much longer than left, reaching anterior third of body; left one short, confined to posterior end. Longitudinal muscles unbranched and cylindrical. No ossicles detected in body wall, gonad and respiratory trees. Ossicles of tube feet usually absent but may include minute spinous rods, either situated at base or tip. Tentacle ossicles as straight or curved spinous rods (Figure 19B).

Distribution. Sub-Antarctic-Antarctic, North and South Pacific Oceans, southern Indian and East Atlantic Oceans and eastern Australian continental slope, 91–1587 m (O’Loughlin & Ahearn 2005).

Remarks. The genus Pseudostichopus was revised by O’Loughlin and Ahearn (2005) who provided a formidable list of synonyms for several of their recognized species. Comprehensive testing of these synonyms awaits further testing. According to their key, the current specimen is identified as P. mollis Théel, 1886 (= P. trachus Sluiter, 1901). Unbranched gonadal tubules characterise this species but in the current material some are distinctly branched at least once dichotomously. However the pygal furrow is indistinct and the tube feet and their distribution also indistinct. Nevertheless, the size of the specimen, its encrustation (Globigerina), minute tube feet, absence of ossicles in the gonad and respiratory trees, and their presence in only the tentacles and tube feet, betrays its specific identity.