Psolidium pawsoni O'Loughlin & Ahearn 2008, sp. nov.

Psolidium pawsoni sp. nov.

Figures 2c; 7a, b

Psolidium incertum.— Gutt, 1988: 1, 3, 23, 27–77.— Gutt, 1991a: 147–153.— Gutt, 1991 b: 315, 320, 324–25 (non Psolidium incertum (Théel, 1886) = Psolidium poriferum (Studer, 1876) below).

Material examined. Holotype: Weddell Sea, Coats Land, Caird Coast, off Brunt Ice Shelf, USARP, R/ V Glacier, cr 2 stn 1, 74°28’06"S 30°31’42"W, 513 m, 24 Feb 1969, USNM 1112364.

Paratypes: type locality and date, USNM E40798 (4); type locality and date, NMV F157430 (2).

Other material: Weddell Sea, 430 m, USNM E33925 (1).

Ross Sea, Tangaroa 0802, 67– 69°S 170°E- 178°W, 329–334 m, NIWA 38273 (1); 329–334 m, NIWA 38281 (1); 137–150 m, NIWA 38604 (1); 300–340 m, NIWA 38624 (6); 547–605, NIWA 39084 (12); 565–920 m, NIWA 39181 (2); 479–480 m, NIWA 39311 (6); 456–540 m, NIWA 45695 (8); 447–455 m, NIWA 45699 (1); Tangaroa 0602, stn 394, 67°S 179°E, 540–600, NIWA 44667 (5).

Enderby Land, BANZARE stn 34, 66°21’S 58°50’E, 603 m, SAM K2342 (2).

Diagnosis. Psolidium species up to 28 mm long; body form elongate, narrow, high; dorsal and lateral scales conspicuous, thin, smooth, up to 2.0 mm wide; dorsal and lateral tube feet inconspicuous.

Sole: outer peripheral single series of smaller tube feet; inner peripheral single series of larger tube feet; lacking mid-ventral (sole) radial series of tube feet.

Dorsal ossicles: multi-layered perforated plates (scales), single-layered marginally; plates frequently with smooth white thickening and reduced/small perforations aligned perpendiculartomargininparallelseries;plateswithreticulate thickening and multi-layered centrally, lacking frequent radiating linear thickenings between marginal perforations; up to 4 tube foot canals per plate; dorsal and lateral tube feet lacking support plates.

Sole ossicles: throughout most of sole rare, small, smooth, thin, irregularly shaped rods and perforated plates, sometimes as regular 4-holed plates with marginal knobs or digitiform projections, sometimes surface knobs, up to 200 μ m long; near margin of sole and peripheral tube feet thicker, irregular, elongate, perforated rod-plates, surface with pronounced linear thickenings (suggesting branched rod origin), up to 420 μ m long, intergrading with oval to elongate thick perforated plates, slightly concave, some with secondary layering, up to 320 μ m long.

Tentacles: largest tentacle trunk ossicles irregular round to oval to elongate, smooth perforated plates, some thin with large perforations, some thicker with smaller perforations, plates up to 550 μ m long, rarely with any secondary layering; few narrow perforated plates, lacking evidence of rod derivation, up to 650 μ m long.

Colour (preserved). Body pale brown to off-white; scales with slightly discontinuous haloes; fine red-brown microscopic flecking over dorsal body.

Distribution. Weddell Sea, 260–795 m (Gutt, 1991 b); Ross Sea, 137-920 m; Enderby Land, 603 m.

Etymology. Named for Dr David Pawson (USNM, Senior Research Scientist), with gratitude for his provision of the opportunity to pursue this research, and appreciation of his constant interest and encouragement.

Remarks. Massin (1992) examined specimens of Psolidium poriferum (as P. incertum) from both the Sub-Antarctic islands of the Indian Ocean and the Weddell Sea, and observed that there were significant differences in the structure of the dorsal scales. He judged that the Weddell Sea material “probably represents another species”. We agree, and refer the Weddell Sea, Ross Sea and Enderby Land material to Psolidium pawsoni sp. nov. Gutt (1988) reported Psolidium incertum (Théel, 1886) from the Weddell Sea, and synonymised Psolidium tenue Mortensen, 1925, with P. incertum. We reject a synonymy of P. incertum with P. tenue (see our treatments of P. poriferum and P. tenue). We assume that the Weddell Sea material seen by Gutt is synonymous with our Psolidium pawsoni sp. nov. from the Weddell Sea, but acknowledge that Psolidium tenue might also occur in the Weddell Sea.

Psolidium pawsoni sp. nov. is distinguished diagnostically by the frequent occurrence on the dorsal and lateral scales of smooth white thickening with consequent reduced/small perforations.