Molpadiodemas constrictus, 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 : 153-157

Molpadiodemas constrictus sp. nov.

Figures 3c–e

Material examined. Holotype. North Atlantic Ocean , Puerto Rico Trench, 20°08'N, 65°27'W, 7086 m, RV Gilliss, 20 Jan 1973, USNM 1022814 .

Paratypes. Type locality and date, USNM 1022815 (20) ; NMV F101857 (5).

Other material. Type locality and date, USNM 1022816 (90) ; NMV F101856 (10).

Description. Up to 62 mm long; body rounded anteriorly, frequently strongly tapered and narrow posteriorly, dorsoventrally depressed, low convex dorsally, flat ventrally frequently with longitudinal median depression, body typically with one rarely two deep transverse constrictions most frequently posterior to calcareous ring, body rounded ventrolaterally sometimes subacute; body wall thick, firm, soft, semi-gelatinous; even cover of very small tube feet all over body, some very thin erect, about 0.2 mm long, some lying on body, cylindrical, thin, typically 0.8 mm long, 0.15 mm diameter, up to 1.5 mm long, rarely contiguous; longitudinal muscles flat, broadly attached, narrow, slightly thickened; no ossicles found.

Colour. Body dark mauve-brown (largest), pale grey-brown to translucent (smallest), largest sometimes with dark red-brown markings dorsally, sometimes with even cover of mauve to brown spots ventrally creating a mottled appearance; largest tube feet body colour, smallest off-white.

Etymology. From the Latin constrictus (drawn together,

contracted), referring to the characteristic deep transverse constrictions on specimens.

Distribution. North Atlantic Ocean, Puerto Rico Trench, 7086 m.

Remarks. The transverse constrictions of the body are growth constrictions. They closely resemble similar growth constrictions observed by one of us (M.O’L) in the fissiparous cucumariid species Squamocnus aureoruber O’Loughlin and O’Hara, 1992 . Emson and Wilkie (1980) listed six fissiparous holothurian species, four of them aspidochirotids. M. constrictus is judged to be fissiparous.

The material was at some stage preserved in formalin solution, which might account for the complete absence of ossicles. Amongst Molpadiodemas species the distinguishing characters of M. constrictus are: body form typically with a transverse constriction; distinct posterior taper; body colour frequently with dark markings dorsally and mottled ventrally; minute thin erect tube feet; absence of ossicles.

Figures

Figure 3. a–b, M. atlanticus (NMV F101845, 210 mm long); a, ventral view; b, small epibiotes on body wall. c–e, M. constrictus sp. nov. (USNM 1022815, paratypes); c, dorsal view (51 mm long); d, ventral view (51 mm long); e, tube feet. f–g, M. crinitus sp. nov. (USNM 1023615, holotype, 96 mm long); f, ventral view; g, ventrolateral tube feet. h, M. depressus, pygal furrow, gelatinous body, lateral brim (NMV F101849). i–k, M. epibiotus sp. nov. (USNM 1008183, holotype, 110 mm long); i, ventral view, posterior taper; j, ventral mouth, epibiote concavities (arrows); k, ventral view, epibiote concavity (left arrow), few tube feet (central arrow). l, M. helios sp. nov., tentacle digits, tube feet (lower right) (USNM E31104, paratype). m–o, M. involutus (NMV F101850, 40 mm long); m, ventral view, serrated margin; n, dorsal anterior view, globigerines attached; o, posterior ventrolateral tube feet.