Cheiraster Studer, 1883

Cheiraster richardsoni sp. nov. Plate 1, Figs. F, H, holotype.

Diagnosis: Abactinal paxillae of both disc and arms having an enlarged central spine. Enlarged subcircular pectinate pedicellariae present on the abactinal surface, on the actinal intermediate areas, and occasionally also on the interbrachial marginal angle.

Description: Abactinal paxillae of disc and arms comprising 8–15 short spinules surrounding the central, enlarged vertical spine, in either a single or a double circle. Several enlarged pectinate pedicellariae on the abactinal surface of the disc (in the holotype there are three). Supermarginal plates forming a conspicuous border, each one broader than long, bearing a dense coat of erect spinules, and the interbrachial ones carry in addition a small erect spine occasionally. In the holotype there are 32 superomarginals in an interbrachial arc. from arm-tip to arm-tip. Inferomarginals broader than long proximally, but becoming longer than broad in the distal part of the arm. The proximal ones carry two (occasionally one or three) erect spines, on the outer surface, as well as the coating of erect spinules.

Actinal intermediate areas small, in the holotype not extending beyond the fourth adambulacral and second inferomarginal. Each intermediate plate bears one enlarged and several small spinules, except for the two interradial plates, which instead each carry five finger-like spines forming the comb of the pectinate pedicellaria. Adambulacral plates with a furrow prominence, bearing 6–8 furrow spines and 5–6 similar spines on the outer margin, together with one enlarged subambulacral spine. Oral plates each carrying about 9 furrow spines, the inner three much enlarged, especially the innermost one. The four suboral spines form a linear series on the actinal surface of the plate, the proximal one enlarged.

Material Examined: The unique holotype, from 400 fathoms, Cook Strait, VUZ Station 87.

Remarks. Cheiraster richardsoni falls in Fisher's grouping of species with an enlarged central paxillar spine, present on both disc and rays. From C. niasicus Ludwig it is distinguished by having pectinate pedicellariae on the abactinal surface, and from C. pilosus Alcock it differs still more, since there are apparently no pedicellariae at all in that species (see Fisher, 1919, p. 195). From C. inops it differs by having paxillae as numerous on the disc as on the arms, and by possessing pedicellariae. One other species, C. trullipes (Sladen) is comparable, as it has large subcircular actinal intermediate pectinate pedicellariae—however, C. trullipes falls in the grouping of species which lack the enlarged central paxillar spine.

Holotype: In the Department of Zoology, Victoria University of Wellington. R 31 mm, r 9 mm.