Molpadiodemas helios, 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 : 160

Molpadiodemas helios sp. nov.

Figures 1a , 3l , 4q–t , 6c, d

Material examined. Holotype. Central Pacific Ocean , Clipperton Fracture Zone, 13°13'N, 129°53'W, 4877 m, RV Governor Ray, Ocean Minerals Co., 15 Feb 1980, USNM E31106 .

Paratypes. Type locality, 13°13'N, 129°52-53'W, 4724–4892 m, 1980, USNM E31104 (1) , E31117 (1), E31134 (1), E31137 (1), E31141 (1), NMV F101852 (1) , F101854 (1).

Other material. Type locality, 13°13'N, 129°52–55'W, 4755–4938 m, 1980, USNM E31097 (1) , E31103 (1), E31105 (1), E31110– E31114 (5), E31118 (1), E31129 (2), E31133 (1), E31138– E31140 (3), E31144 (1), E48515 (1), NMV F101853 (1).

Description. Up to 170 mm long; body wall soft-leathery to semi-gelatinous; no body attachments (encrustations); body rounded in transverse section, lacking brim; tentacles with about 10 large conical pointed digits peripherally, some digits bifid; tube feet soft, white to semi-translucent, scattered and lying all over body, most dense around oral and pygal areas, up to 2.0 mm long, 0.15 mm diameter, frequently cylindrical digitate erect orally and pygally, typically 0.8 mm long, 0.2 mm diameter; ossicles in tentacles and gonad; tentacle ossicles sparse to rare, thick to thin rods up to 150 µm long, rare branches, rare perforations at ends or branches joined to form perforations, lacking spines, sometimes swollen mid-rod; gonad tubules with abundant irregular thin rods, some irregularly branched, branches sometimes joined to create perforations, lacking spines, swellings rare, up to 280 Μm long.

Colour. Body off-white to grey, frequently semi-translucent, smaller specimens sometimes with pale brown.

Etymology. From the Greek helios (sun), referring to the sunflower appearance of the radiating tentacle digits.

Distribution. Central Pacific Ocean, Clipperton Fracture Zone, 13°13'N, 129°53'W, 4724–4938 m.

Remarks. Amongst Molpadiodemas species, the distinguishing characters of M. helios are: relatively prominent soft tube feet scattered over the body, sometimes cylindrical and erect posteriorly and anteriorly; prominent conical tentacle digits; predominantly smooth rod ossicles in gonad.

Figures

Figure 1. Characters of pygal-furrowed Synallactidae. a, ventral mouth and anus (M. helios sp. nov., USNM E31104, paratype, 91 mm long); b, ventral peltate tentacles, polian vesicle (P. mollis, TM H2004; anterior end dissected off); c, respiratory tree (P. mollis, TM H2004); d, drawing of dorsal posterior pygal furrow; e, posterioventral view of pygal furrow and anus (M. violaceus, BMNH 86.10.2.150); f, anterior dorsal madreporite (arrow) (P. peripatus, USNM 1008159); g, drawing of calcareous ring (radial plate right, as in P. spiculiferus); h, calcareous ring (M. crinitus sp. nov., USNM E48644, paratype); i, calcareous ring (M. violaceus, BMNH 86.10.2.145).

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.

Figure 4. Tentacle ossicles (SEM). a–d, Meseres atlanticus, a–c (USNM E49466), d (USNM 1020067). e–h, M. crinitus sp. nov. (USNM E48662). i–l, M. depressus (USNM E53279). m–p, M. epibiotus sp. nov. (USNM 1008310, paratype). q–t, M. helios sp. nov., q–r (USNM E31104, paratype), s–t (USNM E31117, paratype). u–x, M. involutus (USNM E49256).

Figure 6. Gonad ossicles (SEM). a–b, Meseres atlanticus (USNM E53278). c–d, M. helios sp. nov. (USNM E31106, holotype). e–h, M. neovillosus sp. nov. (USNM 1008458, paratype). i–l, M. porphyrus sp. nov. (USNM E38795, holotype). m–p, M. ustulatus sp. nov. (USNM 1022493, holotype).