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

Psolidium whittakeri sp. nov.

Figures 3b-d; 8d-f

Psolidium incertum.— Ludwig and Heding, 1935: 162–64, text figs 28–29 (non Psolidium incertum (Théel, 1886) = P. poriferum (Studer, 1876) (above).

Material examined. Holotype: Scotia Sea, South Sandwich Is, Saunders I., 57°39’24"S 26°26’42"W, 415–613 m, R/ V Islas Orcadas, USARP cr 575 stn 52, 26 May 1975, USNM 1112365.

Paratypes: type locality and date, USNM E40795 (39 specimens); NMV F157431 (6).

Other material: South Sandwich Is, 146–527 m, USNM E40817 (1); 355-468 m, E40818 (1); 302–375 m, E40819 (2); 360–486 m, E40827 (2); 452–759 m, E40828 (1).

Bouvet I., Icefish 2004 stn 59, 408–656 m, NMV F104857 (3); stn 71, 193–207 m, F104867 (1); stn 73, 316 m, F104896 (1); stn 76, 650–646 m, F104837 (7)

South Shetland Is., Elephant I., 326–382 m, AMLR-03 stn 38, NMV F104849 (1); Deception I., 460–484 m, AMLR-03 stn 88, F104834 (3); F104835 (1).

Diagnosis. Psolidium species up to 42 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, multi-layered centrally; reticulate thickenings extend from near margin towards centre of plate, thickenings near margin sometimes parallel to edge of plate, sometimes coalesce into smooth thickenings with smaller perforations, lacking frequent radiating linear thickenings between marginal perforations; up to 4 tube foot canals or marginal indentations per plate; dorsal and lateral tube feet lack support ossicles.

Sole ossicles: throughout sole rare, small, smooth, thin, irregularly shaped rods and perforated plates, 0–9 large perforations, bluntly spined around margin, sometimes surface knobs, up to 260 μ m long; sometimes as regular 4-holed plates with bluntly spined margin, sometimes surface knobs, up to 230 μ m long; near margin of sole and peripheral tube feet thicker irregular rods and elongate perforated rod-plates, up to 420 μ m long, intergrading with some round to oval, perforated thick plates up to 350 μ m long, some with secondary layering.

Tentacles: largest tentacle trunk ossicles; perforated plates, irregularly round to oval to elongate to narrow, thick, smooth, lacking rod-like thickenings between perforations; perforations large, irregular in size, rare incipient secondary developments; plates up to 750 μ m long; rare rod-plates, up to 440 μ m long.

Colour (preserved). Dorsal and lateral body off-white (type material) to pale brown to brown (Bouvet and South Shetland Is material); scales faintly haloed, with pale outer edge (single-layer perforated edge of scales with white thickening); small dark brown markings; sole off-white to pale brown to brown.

Distribution. South Sandwich Is, South Shetland Is, Bouvet I.; 146– 759 m.

Etymology. Named for Scott Whittaker (USNM), with appreciation and gratitude for his generous and gracious assistance to Cynthia Ahearn in preparing SEM images.

Remarks. We judge that the 10 specimens from Bouvet I. (567 m) that were referred to Psolidium incertum (Théel, 1886) (= P. poriferum above) by Ludwig and Heding (1935) do not differ in any diagnostic characters from material from Bouvet I. examined here, and hence from Psolidium whittakeri sp. nov. In particular, the smooth perforated plate form of the tentacle trunk ossicles and the pale brown body and brown sole are the same. The preserved colour of the type material of Psolidium whittakeri sp. nov. (collected in 1975) is off-white. The recent material from Bouvet and the South Shetland Islands (collected in 2003 and 2004) is brown. It is difficult to judge whether this significant colour difference is due to preservation history or species difference. No significant morphological differences have been detected and it remains for current work on molecular genetic evidence to confirm species status. Of the series of poriferum -like species of Psolidium, we recognise that P. whittakeri sp. nov. (Bouvet, South Sandwich, South Shetland Is) is closest to P. pawsoni sp. nov. (Weddell Sea), but judge that there is significantly more frequent development of smooth white thickening on the scales of P. pawsoni. We note also that the P. whittakeri specimens are significantly larger (up to 42 mm long) than the P. pawsoni specimens that were available (up to 28 mm long).