Psilaster acuminatus Sladen

Psilaster acuminatus Sladen, 1889, p. 225, pl. 40, figs. 1, 2, pl. 42, figs. 7, 8; Clark, H. L., 1916, p. 32; —, 1923, p. 248; Mortensen, 1925. p. 274; Fell, s1958, p. 4; —, 1959, p. 131, fig. 13; McKnight, 1967, pp. 292, 298.

Material Examined:

32 specimens, St. 1847 (3); 1848 (27); 1849 (2).

Size:

R = 70–31 mm., average 49 mm.; r = 12–6 mm., average 10 mm.

Remarks:

This species has been well described previously. Sladen (1889, p. 227) records some specimens in which superomarginal spines are present for a short distance page 12along the arms; subsequent authors do not mention this. Of the 32 specimens in this collection, 14 (R/r averaging 47/10 mm.) are without any trace of superomarginal spines; 12 specimens (R/r averaging 52/11 mm.), have occasional, isolated superomarginal spines and 6 specimens (R/r averaging 52/11 mm. also), have an almost continuous row of small distinct superomarginal spines midway along the arms but these are absent proximally from the first 7–9 plates and distally near the arm tips. In other specimens examined by the author, superomarginal spines were present occasionally. Otherwise the specimens agree well with previous descriptions although as Mortensen (1925, p. 275) notes, Sladen's description of the inferomarginal plates is misleading. At least 6 specimens in the present collection, have regenerating arm tips.

Colour:

Dark pink to orange-pink abactinally, regenerating arm tips white; marginal plates yellow or pinkish-white, actinal surface creamy yellow and tube feet delicate pink.

Geographical Distribution:

New Zealand, Australia and ? South Africa (Australian and South African specimens are not available to the author for comparison, but from H. L. Clark's (1923, p. 248) description of South African material, there are differences).

Depth Range:

35–1757 m.

Type Locality:

"Challenger" Sta. 167, 39° 32′ S., 171° 48′ E., north-west of Port Hardy, New Zealand; 277 m.

Location of Type:

British Museum (Nat. Hist.).

Plutonaster fragilis n.sp. (Fig. 1, c, d; Pl. 1, a, b).

Material Examined:

42 specimens, Sta. 1846.

Size:

R = 98–66 mm., average 82 mm.,; r=32–20 mm., average 26 mm.

Description:

Description based on specimen with R/r = 75/22 mm.

Disc large, compressed dorso-ventrally; arms short, tapering evenly to sharp tip protected by saddle-shaped plate.

Abactinal paxillae small, crowded, without regular arrangement except near arm edges where they form transverse rows. Plates oval or faintly lobed, paxillar trunk short with broad expanded head bearing from 10 (near arm margin) to 25 fine rugose spinelets. Occasional inconspicuous pedicellariae, formed by enlarged tips of 3 or 4 paxillar spines, present along arm margins.

Madreporite almost circular, compound, finely dissected, large (about 10 mm.), nearer edge than centre of disc; covering paxillae large, with up to 45 spinelets each.

Supermarginal plates tumid, rectangular, 35 or 36 extending from interradial angle to arm tip, forming distinct border to abactinal surface; plates covered with small spinelets similar to those of abactinal paxillae. Each plate with one, occasionally 2, enlarged, sturdy, tapering, broad-based spines. Plates separated by distinct fascioles lined with thin, blunt-tipped, flattened spines. Inferomarginal plates page 13corresponding to superomarginals, forming broad edge to actinal surface. Plates separated by deep fascioles and bearing generally one (occasionally 2 proximally) enlarged, broad-based tapering spines. Occasional incipient pedicellariae formed by enlarged and clavate heads of 3 or 4 spines, near superomarginals.

Actinal interradial areas extending for at least half length of each arm, plates in regular longitudinal rows, one plate corresponding to each adambulacral and 2 to each inferomarginal. Each plate (fig. c) with numerous short spines; interradially, generally a single (occasionally near oral plates 2) central, enlarged blunttipped spines. Many plates interradially, with distinct pedicellariae (fig. c) formed by enlarged and clavate heads of 3–5 spines.

Adambulacral plates (fig. d) with regular fringe of 9–11 furrow spines; one conspicuous, sturdy subambulacral spine similar to enlarged spines of marginal series, surrounded by number of smaller, spaced spines. Occasional incipient pedicellariae present on outer edge of plates adjacent to actinals.

Oral plates with 10–12 subequal, slender furrow spines and numerous shorter suboral spines arranged in more or less distinct longitudinal rows.

Ambulacral grooves deep, tube feet biserial without distinct sucking discs.

Variations:

Unfortunately much of the remaining material is damaged as the specimens deteriorate very quickly out of water. Most variation seems to occur in the number of actinal and inferomarginal pedicellariae which are always present but which may be few or numerous irrespective of the animals' size.

Remarks:

This new species is characterised by the large number of adambulacral and oral furrow spines and by the presence of abactinal, inferomarginal and actinal pedicellariae (it appears to be the only known species with inferomarginal pedicellariae). P. knoxi Fell from the Chatham Islands is similar but can be distinguished by its rather smaller disc, longer and more slender arms, fewer adambulacral furrow spines (7 or 8) and the lack of pedicellariae. The present species is similar to the North Atlantic P. bifrons Wyville Thomson but the presence of pedicellariae is distinctive; it can be distinguished from P. abyssicola Ludwig (Gulf of Panama) by the more numerous spines of the abactinal paxillae and the presence of generally only one inferomarginal spine.

Colour:

Disc centre white to pale yellow with orange or yellow arms; paxillae covering madreporite lighter than those adjacent; marginal plates orange, spines white. Actinal surface pale orange or yellow, always darker near edge; tube feet and actinostomial membrane orange.

Geographical Distribution:

Known only from the type locality, off the West coast of the South Island, New Zealand.

Depth Range:

1647–1693 m.

Type Locality:

"Eltanin" Sta. 1846, 43° 54′–43° 48′ S., 167° 43–167° 46′ E., off West Coast of South Island, New Zealand; 1647–1693 m.

Location of Type:

United States National Museum.