Psolidium ramum, Davey, 2013

Davey, Nicola, 2013, The Psolidae of New Zealand and some additions to the Macquarie Ridge fauna (Echinodermata: Holothuroidea: Psolidae), Memoirs of Museum Victoria 70, pp. 51-67 : 65-66

Psolidium ramum sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:A9BB906B-094B-

4F5E-83C5-5FFD1C68CC9B

Table 1, Figures 2, 6A–B, 11A–H.

Material examined. Holotype. New Zealand, North Island west coast canyons: NIWA 73660 (1) Stn TAN1105/88, 36.18°S 173.68°E, 188– 210 m, 01/04/2011.

Description. Psolidium species up to 16 mm long, 8 mm wide, 2 mm high. Profile low, body form oval. Oral cone slightly higher than anal cone; no distinct oral or anal valves or plates, approximately 230 µm wide, macroscopically smooth, microscopically glassy and beady texture, lacking significant bumps or pillars. Body wall dorsal and lateral scales macroscopically evident and continuous over body wall, up to 2.3 mm at widest point. Tube feet numerous, up to 10 per scale, evident throughout dorsal and lateral scales. Tentacles 10; 8 + 2 (ventral smaller). Sole largely destroyed, with peripheral single row of larger tube feet and smaller outer non-continuous ring of tube feet; midventral row of tube feet present, only 2 feet found as a result of a damaged sole.

Dorsal and lateral ossicles include large multilayered thick scales with small perforations and conspicuous round tube feet holes up to 60 µm in diameter; numerous tube feet support plates up to 85µm wide; rare single-layered plates with 4–9 perforations up to 70 µm wide; broken thorn (branching rod) ossicles present.

Ventral ossicles knobbed perforated plates up to 100 µm wide with blunt marginal projections, predominantly 4 projections, sometimes more projections peripherally, and thick elongate plates up to 160 µm long, without knobs, with small perforations; small crosses up to 60 µm wide; thorn ossicles present, mainly broken, largest 135 µm.

Colour. Preserved: white, with dorsal and lateral scales, grey centrally.

Distribution. New Zealand, North Island west coast, 188– 210 m.

Etymology. The Latin word ‘ ramum’ = branching, in reference to the branch-like thorn ossicles in the dorsal and ventral body wall of this species.

Remarks. This description is based on one specimen, of which the ventral sole was partially destroyed. The distinctive thorn ossicles, while rare, were present in both the dorsal and ventral body wall and have not been reported for any other New Zealand Psolidium species. In Psolidium ramum sp. nov. the ventral ossicles have predominantly 4 perforations; in P. marriotti sp. nov. they are numerous. P. aequm sp. nov. has larger perforations, thicker ossicles and many more angular knobs on ossicle margins. The thickened elongated plates are unique to P. ramum sp. nov. The northwest Australian species P. parmatus ( Sluiter, 1901) and P. nigrescens Clark, 1938 also contain thorn ossicles similar to those of P. ramum sp. nov., but P. parmatus has bulbous pillars on the dorsal and lateral scales, and P. nigrescens is black, and has cups and crosses ventrally.

Further specimens would contribute to this description. The structure and distribution of ventral tube feet are difficult to determine, and there was little material available for ossicle extraction and SEM study. The tentacle ossicles could not be described due to the damaged state of the specimen, and these will need to be examined in the future.