Psolidium Ludwig, 1886: 9.— Mortensen, 1927: 413.— Deichmann, 1941: 141–43.— Deichmann, 1947: 336.— Lambert, 1996: 21.
Diagnosis (see O’Loughlin and Maric, 2008). Dendrochirotid holothuroids; small, up to 40 mm long; mid-body arched dorsally in transverse section, flat ventrally; dorsal and lateral body covered with imbricating scales, usually macroscopically conspicuous, irregular in size and arrangement; scales decreasing in size ventro-laterally, orally and anally; lacking large oral valves; extensible oral cone, anterior to anteriordorsal to dorsal orientation; extensible anal cone, posterior to posterior-dorsal to dorsal orientation; tube feet dorsally and laterally in mid-body, pass through scales.
Sole distinct, oval to elongate; discrete margin created by junction of small imbricating ventro-lateral scales with thinwalled, usually calcareous, sole that lacks scales; peripheral band of tube feet, may be discontinuous across the inter-radii anteriorly and posteriorly; peripheral tube feet frequently of 2 sizes, outer series smaller; mid-ventral radial series of tube feet present or absent.
Calcareous ring solid, plates sub-rectangular, radial and interradial plates with tapered anterior projections; radial plates with deep notch posteriorly, interradial plates with shallow concave indentation posteriorly; 10 dendritic tentacles, ventral 2 smaller.
Dorsal and lateral ossicles: multi-layered or single-layered perforated plates (scales), always some with tube foot canals; integument covering scales may have cupped crosses, cups, “thorn” ossicles (irregular branched rods pointed distally), buttons, perforated plates and rosettes; tube foot small endplates, and tube foot support ossicles that are irregular rods and plates, bent and curved, variably perforated.
Sole ossicles: inter-radii with small to large single-layered perforated plates (rarely with multi-layering), smooth to variably knobbed and thickened, sometimes with cupped crosses, cups, thorn ossicles, and rosettes; radii with additional tube foot ossicles, large endplates and tube foot support ossicles that are irregular rods and plates, bent and curved, variably perforated.
Tentacle ossicles: perforated plates, rod-plates and rods, thick to thin, long to short, straight or bent, flat or curved; dendritic tentacle branch endplates are small, irregular in shape, cupped, with a few large perforations and irregular margin; densely branched rosettes may be present.
Type species. Psolidium dorsipes Ludwig, 1886.
Antarctic and Sub-Antarctic species. Psolidium disciformis (Théel, 1886); P. dorsipes Ludwig, 1886; P. emilyae sp. nov.; P. gaini Vaney, 1914; P. incubans Ekman, 1925; P. normani sp. nov.; P. pawsoni sp. nov.; P. poriferum (Studer, 1876); P. schnabelae sp. nov.; P. tenue Mortensen, 1925; P. whittakeri sp. nov.