Deep-Sea Echinoderms of New Zealand
Pseudarchaster Sladen, 1885
Pseudarchaster Sladen, 1885
Abactinal plates paxilliform, extending far along the arm in several series, usually more than one series reaching the terminal plate. An unpaired median but not recurved tooth common to each pair of oral plates. Adambulacral armature comprising a palmate group of furrow-spines and a co-ordinate group of subambulacrals. Numerous actinal intermediate plates. Marginal plates thick, robust, paired, with fasciolar grooves between them.
Pseudarchaster, though widely distributed, has not hitherto been discovered in New Zealand or Australia ("Pseudarchaster" boardmani Livingstone, of New South Wales, must be referred to Mediaster, as H. L. Clark (1946) has already shown). One deep-water species can be recorded from Cook Strait, and, by an unusual coincidence, a second sublittoral species has become known at the same time from the same area. For the sake of clarity both species will be diagnosed here, though only one of them is so far known from below the continental shelf.
|Superomarginals, inferomarginals and actinal intermediate plates bearing granules, without enlarged spinules. Abyssal||P. garricki|
|Superomarginal plates bearing granules, but inferomarginal and actinal plates bearing both granules and coarse spines. Sublittoral||P. abernethyi|
Pseudarchaster garricki sp. nov. Plate 3, Figs. G, K, holotype.
Description: Abactinal paxillae in crowded hexagonal or polygonal groups, largest on the disc, comprising usually about 7 polygonal granules closely arranged around a central polygonal granule, and with small angular grains filling in the outer margins of the paxilla.page 9
A, B, Peribolaster lictor sp. nov.; A, abactinal skeleton and armature, midway along arm of holotype; B, oral, adambulacral and inferomarginal plates. C, Allostichaster insignis var. gymnoplax var. nov., supermarginal and inferomarginal plates. D, E, H, Cosmasterias dyscrita H. L. Clark; D, unguiculate (felipedal) pedicellaria from oral plate; E, adambulacral and actinolateral plates and their armature; H, oral plate, oriented so that the distal suboral spines are lowermost. F, Crossaster japonicus (Fisher), adambulacral plates and one inferomarginal, showing armature. G, I, Pteraster (Apterodon) bathami sp. nov.; G, oral plates and first three adambulacral wings, showing armature; I, paxillar spinules and webs of aboral surface.
Marginals broad and short, the proximal ones about four times as broad as long. About 40 marginals from the interradius to an arm-tip. Both superomarginals and inferomarginals covered in a uniform, dense granulation of more or less hexagonal granules. No scales or spinules on any of the marginals. Adambulacral plates with an armature of 5 or 6 truncate, compressed furrow-spines, and 7 or 8 truncate subambulacral spines, similar to the furrow spines, but not compressed. Distad to these is another line of finer spines, 4–5 in number. These form a postadambulacral fasciole, in conjunction with a still finer series of spines carried on the proximal margin of the proximal intermediate plate. The intermediate plates otherwise bear only granules, with no enlarged spines.
Material Examined: Only the holotype, which is from 550 fathoms in Cook Strait, VUZ Station 101.
Remarks: P. garricki is apparently distinguished from all other species of Pseudarchaster by the complete absence of spines or spinules from the uniformly granulated marginals and actinal intermediate plates.
Holotype: In the Department of Zoology, Victoria University of Wellington. R 82 mm, r 26 mm. Rays 5. Colour in life, orange above, cream below.
Pseudarchaster abernethyi sp. nov. Plate 3, Figs. I, J, holotype.
Description: Abactinal paxillae in crowded hexagonal or polygonal groups, largest on the disc, tending to become transversely rectangular at the bases of the arms. On the disc the paxilla comprises usually about 30 granules, the central ones more markedly polygonal than the outer ones, which tend to be rounded, and are packed less tightly. Marginals broad and short, the proximal ones about three times as broad as long. About 42 marginals from the interradius to the arm-tip. The superomarginals covered in a rather fine, more or less uniform granulation, somewhat coarser toward the outer edge, and with the fascioles between the plates formed by finer granules in linear series. The inferomarginals densely covered in a scaly granulation, with occasional lanceolate, flattened spines directed distally from short stalks. Adambulacral plates with an armature of 3–6 (usually 4 or 5) cylindrical truncate furrow-spines, and about 12–16 truncate, cylindrical or compressed subambulacral spines; one of the subambulacral spines is usually much expanded into a flattened, or bifurcate, or sometimes lanceolate spine. Postambulacral fascioles indistinct. Intermediate plates armed with irregular granules, spines and occasional enlarged lanceolate spines, the borders defined by delicate spinules, arranged too irregularly to form obvious fascioles.
Material Examined: Fourteen specimens, including the holotype, from 55–63 fathoms, 10 miles E. by S. of Cape Campbell, March, 1957. Coll. F. Abernethy.
Remarks: From P. garricki this species is easily distinguished by the spines on the inferomarginal and actinal plates. P. abernethyi does present some close parallels to some other species, however. In particular it appears to fall close to P. parelii (Düben & Koren), a circumpolar north Pacific and north Atlantic species. To judge by Fisher's (1911) account, P. parelii has smaller paxillae, since the larger ones described by him have only half the number of granules found in P. abernethyi; this difference is further confirmed by Plate 31 in Fisher's book, a photographic plate which is clear enough to enable the granules in the paxillae to be counted. The material of P. abernethyi at my disposal shows considerable variation, especially as regards the adambulacral and actinal intermediate armature, but all specimens agree in having the larger type of paxilla which is present in the holotype. I therefore regard this as a primary diagnostic character. Pseudarchaster discus Sladen, from the Magellanic area, also invites comparison, but here again the paxillae are even smaller, having only "about a dozen" polygonal granules, according to Sladen (1889, p. 111). From P. dissonus Fisher the absence of bivalved postadambulacral pedicellariae provides a distinguishing feature, and the furrow-spines of P. dissonus are sharp, not truncate.
Holotypes In the Department of Zoology, Victoria University of Wellington. R 110 mm, r 32 mm. Rays five. Colour in life, orange above, the actinal surface cream.