Trachythyone mackenzieae O'Loughlin, 2009, sp. nov.

Trachythyone mackenzieae sp. nov.

Figures 2 f, 3b, d, f; table 1.

Material examined. Holotype. Eastern Antarctica, Prydz Bay, Fram Bank, 67°25'S 70°20'E, 161–165 m, ANARE AA91 stn 94, C.C. Lu & T.N. Stranks, 26 Feb 1991, NMV F68073.

Paratypes. Fram Bank, 67°31'S 69°02'E, 105–114 m, AA93 stn 130, M. O’Loughlin, 13 Feb 1993, NMV F68668 (1); off Kaiser Wilhelm Land, 65°48'S 89°49'E, 393 m, BANZARE stn 100, 3 Feb 1931, SAM K2451 (1).

Diagnosis. Body elongate, fusiform, slightly tapered and rounded posteriorly; up to 60 mm long (preserved, excluding tentacles); body wall calcareous, rugose, not parchment-like; 10 dendritic tentacles, ventral pair small; tube feet in radial series, retractile, dorso-lateral radial series variable size, zig-zag to double discontinuous rows, 3 ventral radial series close zig-zag to double irregular rows; calcareous ring lacking posterior prolongations, radial plates with narrow sub-rectangular anterior projection, interradial plates with strongly tapered anterior projection, all plates with rounded notch posteriorly; single polian vesicle; gonad tubules long, thin, unbranched.

Mid-dorsal body wall ossicles thick perforated plates, spinous cups; plates irregularly oval to elongate, predominantly more than 2 perforations wide, plates up to 528 µ m long, lacking knobs over most of plate, but frequently knobs, spines and thick low spinous spire above one end of surface of plate, about 160 µ m high; irregular deep to shallow cupped crosses and cups, 48–88 µ m long, blunt to pointed spines on rim, 4–8 perforations, perforations frequently small, no cups closed by bridges across rim. Tentacle ossicles rodderived perforated plates, round to oval to elongate, curved to bent to cupped, thick blunt margin and surface spines, plates up to 536 µ m long.

Distribution. Eastern Antarctic coast, 70°–90°E, 105– 393 m.

Etymology. Named for Melanie Mackenzie, Museum Victoria Research Associate, with appreciation of her valuable assistance in determining Antarctic holothuroid material.

Remarks. The distinguishing diagnostic characters of Trachythyone mackenzieae sp. nov. amongst Antarctic and Sub-Antarctic Trachythyone species (T. bouvetensis, T. cynthiae sp. nov. (above), T. maxima and possibly T. parva) are: calcareous rugose surface; paired radial series of retractile tube feet; thick spinous spires arising above one end of body wall plates.