Psolidium nigrescens H. L. Clark

Psolidium nigrescens H. L. Clark, 1938: 505-507, fig. 50.—H. L. Clark, 1946: 414–15.— Cannon and Silver, 1987: 29.—Rowe (in Rowe and Gates), 1995: 318.

Material examined. New South Wales, Broken Bay, Hawkesbury River, Yeomans Bay, Smith-MacIntyre Grab, mud sediment, G. Phillipson, Oct 1992 (specimen not lodged in museum) ; Port Jackson, Middle Harbour, N bank W of Spit Bridge, 33°48'S 151°15'E, steeply sloping bottom with telestacean bed, live and dead mussels, Tethia sp. and compound ascidians, 8 m, J. K. Lowry, 9 Jun 1981 , J24097 (1); Botany Bay, off Dolls Point, dredged, 7–11 m, D. F. McMichael, Oct 1949 , J6789 (4); Port Hacking, Gunnamatta Bay, 34°04'30"S 151°08'54"E, on shells of Anadara, I. Bennett, 2 Nov 1948, AM J6821 (6) ; Batemans Bay, Clyde R, edge of channel near southern bank downstream from Princes Hwy road bridge, 35°42'34"S 150°11'3"E, 5 m, clump of hairy mussels, Australian Museum party, 30 Mar 2004 , J24092 (3).

Description. Psolidium species up to 40 mm long (preserved); body elongate; dorsal and lateral body scales thick, up to 4 mm wide, covered by fairly thick integument; scales tapered to projecting rounded point orally and anally; dorsal and lateral tube feet conspicuous, up to 5 pass through a scale.

Sole with peripheral band of tube feet, about 5 wide, outermost tube feet not smaller; mid-ventral radial series of tube feet predominantly 2 wide.

Dorsal and lateral ossicles: multi-layered ossicles (scales) with tube foot canals; thick knobbed buttons, 3-10 perforations, up to 192 μ m long, intergrade with multi-layered ossicles; branched rods with pointed ends (“thorn” ossicles), irregular form, 3-5 arms, flat to 3-dimensional, up to 56 μ m long; rosettes, densely branched, up to 40 μ m long.

Sole ossicles:perforated plates, slightly concave, irregularly round, knobbed marginally, up to 14 perforations, up to 152 μ m long; very shallow, marginally knobbed, 4-perforation cups and cupped crosses, typically 96 μ m long; rare rosettes; rare “thorn” ossicles.

Tentacle ossicles include: rosettes, up to 40 μ m long; “thorn” ossicles, up to 40 μ m long.

Colour (preserved). Dorsal and lateral body black to brown to dark grey, with fine white spotting over scales; tube feet off-white; sole pale brown to cream, with some fine brown flecking; tentacle trunks dark brown, tentacle dendritic ends off-white.

Distribution. Eastern Australia, central New South Wales, Broken Bay to Batemans Bay, estuarine; 0– 11 m.

Remarks. The distinguishing characters of Psolidiumnigrescens H. L. Clark, 1938 are the “thorn” ossicles in the body wall, and very dark brown to black colour.