Psychropotes sp.

Psychropotes sp. MoV. 7327

Figure 22a–j, Appendix 1, Table S1

Material examined. NMV F308272 About NMV (1) [IN 2022 V 08 147] .

Diagnosis of IOT material. Large purple specimen with unpaired dorsal appendage, preserved ~ 190 mm long, 90 mm wide

(including brim) and 20 mm high. Raised and slightly rounded dorsally, flattened ventrally, surrounded by a very broad brim (20–40 mm in live specimen) of enclosed tube feet that gives the animal a wide flattened appearance. Unpaired dorsal appendage opaque pink and positioned approximately one third of the way from posterior end. Flaccid and gelatinous with almost square end, lobed on the tip of each side. Lobes are very small, only ~ 5 mm in fresh specimen and completely retracted in preserved; darker red lines (presumably canals) leading to them suggest that they are inflatable/extendable. Appendage was approximately one fifth the length of the body before preservation, but closer to quarter the length (~ 50 mm long) after, presumably due to contraction of the brim reducing the body size. Skin soft and smooth to wrinkled (no warts), thicker ventrally. Light purple to pink or cream dorsally, brim opaque purple with rust-coloured patches. Anus terminal ventral (under brim). Mouth ventral. Approximately 17 retractile peltate tentacles with marginal knobs on discs. Midventral retracted tube feet along a rust-coloured furrow in paired to zigzag row. Up to four pairs of reduced dorsal papillae, longest pair posterior and ~ 5 mm. Dorsal body wall ossicles (fig. 22d–f) are cross-shaped with four arms and one smooth central spine-like apophysis (e.g. 169 μm). Similar in dorsal appendage (fig. 22g –j) and papillae. Arms directed down, but length and shape quite variable. Some crosses with long tapered arms strongly curved from close to central spire, others slightly more robust with arms starting as a horizontal beam before they splay out and down. Arm length variable (e.g. 200–380 μm in body wall and up to 486 μm in dorsal appendage). Minutely spinous, particularly at ends, but each arm also has (typically one or more) larger vertical spines (e.g. 59 μm) at a short distance from the central spire and occasionally some extra serrations projecting from the dorsal surface. Some similar ossicles in lateral brim, along with reduced crosses. Only variable spinous rods seen in ventral samples (e.g. 360 μm) and tentacles (e.g. 400 μm).

Remarks. External morphology closest to Psychropotes belyaevi Hansen, 1975 with the wide brim, bipartite lobe, reduced tentacle number, and longer papillae posteriorly, but appendage is shorter in this specimen than for P. belyaevi and only lobed at the tips rather than for most of its length, has 17 rather than 16 tentacles, at least four (rather than three) pairs of papillae, and a wider brim. Ossicles are also closer to P. depressa with arched crosses with minimal spines and single central apophyses, compared to the robust crosses lacking apophyses and rings of spines in P. belyaevi .

Not a match for other Australian species – P. longicauda Théel, 1882 and P. scotiae Vaney, 1908 – when compared to Mark O’Loughlin’s (2018) notes, original descriptions, or the Galathea Report ( Hansen, 1975) . Kept at OTU level Psychropotes sp. MoV. 7327 for now until further literature review and genetic investigation can be conducted.

Distribution. This specimen lot only: Indian Ocean, Australian IOT, Cocos (Keeling) Islands Territory, Noel Seamount Stn., 2617–2721 m.

References. Hansen (1975), O’Loughlin (notes and personal correspondence, 2018), Théel (1882), Vaney (1908).