Molpadiodemas sp.

Molpadiodemas sp. MoV. 7334

Material examined. NMV F296842 About NMV * (1) [IN 2021 V04 007] ; NMV F296856 About NMV * (1) and NMV F296859 About NMV * (3) [IN 2021 V04 028] .

Diagnosis of IOT material. Variably oval to elongate sub-cylindrical specimens, dorsally low convex and rounded, ventrally flattened. From small at ~ 3 cm long ( NMV F296842) to large at ~ 15 cm long, 7 cm wide, and 4.6 cm high ( NMV F296856, pre-preservation). Soft to firm, gelatinous, opaque to semitranslucent, off-white to cream-brown with some yellow staining ventrally. Mouth ventral, with ~20 peltate cream to orange-brown tentacles. Anus ventral with pygal furrow. Lateral edges are wavy or bumpy rather than completely smooth. Patchy covering with sand and forams, more condensed mid-ventrally, present on all but not as much on NMV F296842. Tube feet can be inconspicuous but are small, cream-brown, and filamentous when seen in water, not restricted to radii, but particularly dense and matted ventrolaterally (fig. 32f). More obvious on the other specimens once preserved, condensed ventrolaterally and anteriorly. Specimens look and feel much more like each other once preserved. All off-white to grey and shrink on preservation (e.g. 11 cm long, 5.9 cm wide, 2 cm high, NMV F296856), and skin can form a more defined lateral line, though not a true brim. The orange-yellow staining was retained on the ventral side for NMV F296856, particularly at the oral end. Tube feet of all specimens lay flat rather than projecting out. Tentacle ossicles smooth straight to curved rods with and without central thickening (~120 μm), and more typically longer straight to curved rods with some twisting, mesh, or perforations, more typically ~160–240 μm, but up to 400 μm.

Remarks. Specimens do not clearly group together based on pre-preservation morphology, the large and firm NMV F296856 appearing quite different to the much more gelatinous NMV F296859. However, a lack of brim combined with matted hair-like tube feet take all these specimens to Molpadiodemas villosus using the key in O’Loughlin and Ahearn (2005), and tentacle ossicles fall within the types imaged and described. They differ from the species description of M. villosus in the same paper (specimens up to 11 cm) by the clear presence here of globigerine and other attachments, and no gonad ossicles were observed from minimal sampling. Specimens also partially fit ossicle images and description of M. involutus , though lacked obvious raised protuberances and were not a match to specimen image (fig. 3m –o in O’Loughlin and Ahearn, 2005). These IOT specimens currently group in a lineage with M. crinitus , M. involutus , and M. villosus (as noted in Remarks for the genus), so additional morphological and phylogenetic work is required before firm species distinctions can be made. We identify IOT material here to OTU Molpadiodemas sp. MoV. 7334.

Distribution. These specimen lots only: Indian Ocean, Australian IOT, Christmas Island Territory, Christmas Island SE Stn. and Karma Seamount Stn., 2760–3345 m.

References. O’Loughlin and Ahearn (2005).