Molpadiodemas depressus ( Hérouard, 1902 ) O'Loughlin & Ahearn, 2005

O'Loughlin, P. Mark & Ahearn, Cynthia, 2005, A review of pygal-furrowed Synallactidae (Echinodermata: Holothuroidea), with new species from the Antarctic, Atlantic and Pacific oceans, Memoirs of Museum Victoria 62 (2), pp. 147-179 : 158-159

publication ID	https://doi.org/ 10.24199/j.mmv.2005.62.5
persistent identifier	https://treatment.plazi.org/id/116087F5-FFA3-FFEC-FF35-7F15FD56187B
treatment provided by	Felipe
scientific name	Molpadiodemas depressus ( Hérouard, 1902 )
status	comb. nov.

Treatment

Molpadiodemas depressus ( Hérouard, 1902) View in CoL comb. nov.

Figures 3h View Figure 3 , 4i–l View Figure 4

Pseudostichopus depressus Hérouard, 1902: 15–16 , pl. 2 figs 15–18. Platystichopus depressus .— Heding, 1940: 353–358.

Holotype. North Atlantic Ocean , between Portugal and the Azores, 4360 m, Monaco stn 753, 1896, MOM (cannot be located).

Material examined. North Atlantic Ocean, West European Basin, 4426–4435 m, USNM 1005343 (2); NMV F101849 (1); NE of Bahamas, 4383–4558 m, USNM 1008242 (1); E53279 (21); NMV F101868 (4); Sargasso Sea, 5690 m, USNM E49454 (1); N of Puerto Rico, 5248–5278 m, USNM 1008241 (2).

Provisional (very damaged): Gulf of Mexico, 1353–1399 m, USNM E48661 About USNM (1).

Description. Up to 100 mm long, not tapered; body wall gelatinous, thick, firm to soft; sometimes with globigerine attachments; flat ventrally, low convex dorsally, dorsoventrally depressed; thick rounded ventrolateral brim; mouth anterioventral; dorsally smooth to wrinkled, ventrally wrinkled, pustulose; small soft tube feet all over body, thick cylindrical not thread-like, most concentrated and largest orally and pygally, up to 1.0 mm long, 0.3 mm diameter, inconspicuous and dome-like over rest of body, 0.2 mm diameter, closer ventrally than laterally and dorsally; longitudinal muscles flat, slightly thickened, narrow; ossicles in tentacles, large, thick to thin, curved to straight rods, smooth or with few blunt to sharp spines, some with mid-rod swelling, some with branched intertwined ends creating perforations, some irregularly tuberous and rugose, some thickly bifurcate at ends, some with one or two large perforations, no lateral perforations or mesh, up to 390 Μm long.

Colour. Body grey to off-white; tube feet off-white.

Distribution. North and South Atlantic Ocean, West European Basin, Sargasso Sea, off Bahamas and West Indies; 1353–5690 m.

Remarks. The holotype of P. depressus cannot be located (M. Bruni, MOM, pers. comm.), and has been missing for a long time. Belloc (1950) noted the absence when creating a catalogue of types, and there is no slide in Cherbonnier’s comprehensive collection (F. Solis-Marin, pers. comm.).

Based on the description and figures of Hérouard (1902), the characteristics of P. depressus are: up to 74 mm long; off-white colour; pygal furrow; dorsoventrally depressed; thickened lateral brim extending around oral end; distinct dorsal madreporite plate; numerous inconspicuous tube feet all over body; narrow longitudinal muscles; two tufts of gonad tubules; lacking ossicles in body wall and gonads.

In this work numerous North Atlantic specimens are judged to be conspecific. Three were taken from the West European Basin at 4426–4435 m, a locality close to the type locality for P. depressus (between Portugal and the Azores, 4360 m). The conspecific material is characterized by an off-white colour, close cover of very small tube feet, absence of gonad ossicles, dorsoventral depression, and frequently a thick brim. No dorsal madreporite similar to that observed and illustrated by Hérouard (1902) for P. depressus has been seen. But the external evidence of a dorsal madreporite has been rare in this work, and not observing it is considered to be not significant diagnostically. Hérouard (1902) illustrated tufts but not series of gonad tubules (it is not possible to judge branching or not), and illustrated cylindrical longitudinal muscles. On the basis of the consistency of the diagnostic characters of Molpadiodemas (above), it is anticipated that the longitudinal muscles were broadly attached to the body wall, and that the gonad tubules were branched.

Heding (1940) erected the monotypic genus Platystichopus for the species depressus , and referred Platystichopus with Benthothuria Perrier to the Benthostichopodinae (subfamily of the Gephyrothuriidae ). P. depressus has a distinct pygal furrow, has a close cover of minute tube feet, and lacks body wall ossicles. It shares more significant diagnostic characters with Molpadiodemas than Benthothuria , and is referred here to Molpadiodemas . Platystichopus is a junior synonym of Molpadiodemas (see above).

On specimens of M. depressus there are ventral minute red to violet conical attachments similar to those found on M. atlanticus , and considered here to be epibiotes. Amongst Molpadiodemas species the distinguishing characters of M. depressus are: thick gelatinous grey to off-white body wall; dorsoventrally depressed body form; ventrolateral brim; thick cylindrical small tube feet; absence of gonad ossicles.