Psychroplanes convexa ( Hansen, 1975 )

Mackenzie, Melanie, Davey, Niki, Burghardt, Ingo & Haines, Margaret L., 2024, A report of sea cucumbers collected on the first dedicated deep-sea biological survey of Australia’s Indian Ocean Territories around Christmas and Cocos (Keeling) Islands (Echinodermata: Holothuroidea), Memoirs of Museum Victoria (Mem. Mus. Vic.) 83, pp. 207-316 : 222

Psychroplanes convexa ( Hansen, 1975)

Peniagone convexa Hansen, 1975: 135–136 , figs 57–58, 95: 1, pl. 10: 4–5.

Psychroplanes convexa . — Gebruk, 1988 (in Russian): 917.

Material examined. NMV F308185 (1) [IN 2022 V 08 115] ; NMV F308230 (1) [IN 2022 V 08 122] ; NMV F308284 * (1) and NMV F308285 (1) [IN 2022 V 08 151] .

Diagnosis of IOT material. Preserved specimens soft, ovoid, opaque to cream or light purple to grey. Dorsally high and curved, ventrally flattened with sole. All specimens damaged but similar “pig shape” to Amperima . Length: width ratio ~2:1, up to 10 cm long and 5 cm wide ( NMV F308284 , preserved). Anterior velum damaged but broad and thick. Mouth ventral, up to ten tentacles with soft often folded discs, lobed at edges, on short/ thick stalks. Large discrete tube feet bordering ventral sole (>5 each side). Skin a little rough/prickly due to cross-shaped ossicles. Cross-ossicles of variable size and predominantly two types. Slender type with four horizontal base arms originating from the centre, and four shorter horizontally directed apophyses, giving the appearance of a small cross on top of a large one when viewed from above (fig. 10e). Arms are smooth with typically bluntly spinous ends (fig. 10f). More robust cross-ossicles, less regular than the slender type, with four outwardly projecting arms, slightly curved up at end and variably spinous (fig. 10g –j). Arms and four shorter vertical, straight to outward-curving apophyses originate from a square-like centre. Tentacles and tube feet similar, with some rods also seen .

Remarks. Presence of true cross ossicles with arms arising directly from centre place these specimens in Psychroplanes rather than Peniagone . Morphologically also like Psychroplanes obsoleta ( Hérouard, 1899) , which has not been recorded for the Indian Ocean, but more than five pairs of tube feet places this in Psychroplanes convexa ( Hansen, 1975) . Minute dorsal pair of papillae behind anterior velum not seen in these damaged specimens. All specimens have ossicles matching the original P. convexa description and illustrations ( Hansen, 1975), though NMVF 308284 (fig. 10e–g) and NMVF 308285 (fig. 10h–j) are the most typical, with some Peniagone -style ossicles seen in tentacles for NMVF 308230 and some more irregular and spinous versions of robust crosses in NMVF 308185. There is insufficient resolution in the COI data to confidently determine its phylogenetic placement within Elpidiidae (fig. S1).

Distribution. Indian Ocean: off east Africa to Sri Lanka, Australian IOT.

Full bathymetric range. 2973–4990 m (IOT 2973–4990 m).

Type locality. Indian Ocean , between Madagascar and Mombasa, and off Sri Lanka, 4040–4820 m .

This species and genus not previously recorded from Australia in AFD or ALA (accessed January 2024). This IOT material represents a geographic and bathymetric range extension for the species and the first record for Australia .

References. AFD (2024), ALA (2024), Gebruk (1988), Hansen (1975)