Psolus byrdae O'Loughlin & Whitfield, 2010, sp. nov.

Psolus byrdae sp. nov.

Figures 1 a–f.

Material examined. Holotype. Antarctica, Amundsen Sea, Marie Byrd Seamount, 69.2ºS 117.5ºW, 2214 m, BAS BIOPEARL stn BI 07–AGT–2000, K. Linse et al., 15 Mar 2008, NMV F168626.

Paratypes. Ross Sea, Scott I. Bank, 516–595 m, USNM 1132854 (11).

Other material. Scotia Sea, South Georgia, 56º18–23'S 37º04–37'W, 3413–3446 m, USNM 1132855 (2).

Diagnosis. Psolus species up to 28 mm long, 5 mm high, 12 mm wide (holotype); elongate oval form, low vertical profile, lacking oral and anal cones; scales imbricating, macroscopically smooth, microscopically finely beaded, irregular shapes, large and small, rounded and angular, mosaic arrangement, up to 5 mm wide, small near ventral margin; lacking 5 discrete oral valves, oral scales numerous, digitiform or narrow pointed or triangular pointed; tentacles 10, 8 large, 2 small ventrally; calcareous ring with digitiform radial and interradial anterior projections, radial projections larger, concave radial and interradial posterior indentations; thin non-calcareous sole, single to zig-zag series of larger inner peripheral tube feet, widely separated from outer peripheral series of smaller tube feet, lacking mid-ventral tube feet, wide calcareous margin comprising large dorsal and small ventral plates between larger and smaller tube feet series; gonad tubules unbranched.

Dorsal and lateral multilayered ossicles only. Central sole with rare irregular smooth cross-like ossicles and plates, cross branches sometimes joined distally to create small plates with up to 6 perforations, cross-like ossicles commonly 120 µ m long, perforated plates up to 208 µ m long. Margin of sole with numerous crosslike ossicles and perforated plates, up to 144 µ m long; elongate, narrow, perforated tube foot support plates, bluntly denticulate on concave margin, up to 400 µ m long; thick, irregular, rods and perforated plates, sometimes thick knobs on margin and surface, up to 320 µ m long. Largest tentacle ossicles irregularly oval and rounded triangular perforated plates, up to 424 µ m long, surface smooth, bluntly denticulate margin, commonly 2 large and 2 smaller perforations in cross formation in centre of plate.

Colour (preserved). Off-white with pale and dark brown flecking; sole is yellow, transparent, with narrow dark brown border inside the peripheral series of larger tube feet.

Distribution. Antarctic Ocean, Amundsen, Ross and Scotia Seas, 516–3446 m.

Etymology. Named after the Marie Byrd Seamount from which the holotype for this deep Antarctic psolid species was taken. Marie Byrd Land, near the Amundsen Sea, was claimed for the United States by Richard E. Byrd in 1929 and named in honour of his wife Marie.

Remarks. Psolus byrdae sp. nov. has been found at great depths in the Antarctic Ocean, and has not been found on the continental shelf of Antarctica. It is distinguished morphologically from all other Antarctic Psolus species by a combination of: consistently low vertical profile; absence of discrete oral valves; wide calcareous ventral margin around the sole; irregular thick knobbed rods, plates, and numerous smaller crosslike ossicles and plates around the margin of the sole; rare smooth cross-like ossicles and plates in the central sole; lacking ossicles other than scales dorsally and laterally.