Molpadiodemas sp.

Molpadiodemas sp. MoV. 7335

Material examined. NMV F296882 About NMV * (1) [IN 2021 V 04 050] .

Diagnosis of IOT material. Small, soft, dorsoventrally flattened, approximately 65 mm long and 40 mm wide (live). Gelatinous and translucent to cream-coloured with central cavity visible. Grey colour, wrinkled, and soft once preserved. Mouth ventral, with orange-brown tentacles. Anus ventral with yellow pygal furrow. Lateral edges are folded and wavy or bumpy rather than smooth. Tube feet small and filamentous, not restricted to paired radii, but more condensed and matted ventrolaterally, easier to observe in water. Patchy covering of sand dorsally and laterally, more concentrated midventrally. Specimen remained soft but shrank on preservation to 50 mm long, 32 mm wide and 15 mm high. Tube feet are flaccid and lie flat rather than sticking out, lateral edges flattened and rounded, but presumably not a brim as there is no clear differentiation from sole. Longitudinal muscles are flat and broadly attached to the inner body wall, but appear divided. Ossicles in tentacles distinct mesh plates rather than rods, not uniform in size or shape, sometimes with two or more larger perforations, variable, but up to 192 μm long.

Remarks. Longitudinal muscles are flat and attached like Molpadiodemas , not rounded like Pseudostichopus , but unlike the genus diagnosis appear divided here. Again, based on the key and thin, hair-like tube feet this is identified as M. villosus , the only other option being M. porphyrus , which is violet in colour and looks distinctly different ( O’Loughlin and Ahearn, 2005, fig. 5). However, differs from M. villosus in tentacle ossicles and by being more dorsoventrally flattened, translucent and with partial sand cover. Quite different to previous specimens Molpadiodemas sp. MoV. 7334, but a closer match (from live image of NMV F296854) to Molpadiodemas sp. MoV. 7329. No match to distinguishing characters for any of the species outlined in O’Loughlin and Ahearn (2005). Tentacle ossicles look closest to the description of “lace-mesh” tentacle ossicles of M. pustulosus , though those are considered more rod- than plate-like. No obvious nipple-like pustules on the ventrolateral margin also exclude it from this species. While divided flat longitudinal muscles and plate-like tentacle ossicles combined with external morphology indicate this is a new species, the superficial similarity to Molpadiodemas sp. MoV. 7329, along with variable characters within the group, means that extensive additional morphological and phylogenetic work is required. We identify the specimen here as OTU Molpadiodemas sp. MoV. 7335.

Distribution. This specimen lot only: Indian Ocean, Australian IOT, Christmas Island Territory, Balthazar Seamount Stn., 2289–2358 m.

References. O’Loughlin and Ahearn (2005).