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Odinia and Ophidiaster (Asteroidea) in New Zealand

Family Linckiidae — Ophidiaster Agassiz, 1835

Family Linckiidae
Ophidiaster Agassiz, 1835

Type Species. Asterias ophidiana Lamarck

Key to the New Zealand Species
1 (2) Granules present between the adambulacral furrow spines on the surface bordering the furrow kermadecensis Benham
2 (1) No granules between the adambulacral furrow spines on the surface bordering the furrow macknighti n.sp.
page 2
Figs. 1–4.—ophidiaster macknighti n.sp. 1.—A typical alveolate (excavate) pedicellaria. 2.—Madreporite. 3.—The anus, protected by a number of enlarged granules. 4.—Portion of actinal surface, showing the oral and adambulacral plates, the arrangement of the pedicellanae and the covering granules which obscure the outlines of the plates.

Figs. 1–4.—ophidiaster macknighti n.sp. 1.—A typical alveolate (excavate) pedicellaria. 2.—Madreporite. 3.—The anus, protected by a number of enlarged granules. 4.—Portion of actinal surface, showing the oral and adambulacral plates, the arrangement of the pedicellanae and the covering granules which obscure the outlines of the plates.

Ophidiaster macknighti n.sp. (Plate 1, figs. 1-4)

Diagnosis. From the small disc, the more or less cylindrical arms taper only in the last fifth of their length and each terminates in a perfectly smooth plate. Each of the eight papular areas contains from two to eight papulae. The pedicellariae are of alveolate (or excavate) type, very distinct and regularly arranged with spindle-shaped alveolae and tapering jaws. No granules occur on the inner furrow surface of the adambulacral furrow spines.

Description. The disc is small and slightly convex; the five arms are cylindrical and taper fairly rapidly only in the last fifth of their length, the arm tip being protected by a conspicuous, perfectly smooth, hemispherical plate.page 3 There are two more or less regular series of triangular abactinal plates on each arm and these continue, rather irregularly, onto the disc; both these plates and those of the marginal and actinal series are covered by a thick skin in which are embedded numerous, small, irregularly-shaped and irregularly-arranged pin-head-like granules, all of similar size, which totally obscure the outlines of the plates; near the arm tips, however, the granules may be absent and the bare plates visible.

The alveolate (or excavate) pedicellariae (Fig. 1) are conspicuous and slightly raised, occurring in longitudinal rows between the plates of the arms, margins and actinal surfaces; on the disc the arrangement is irregular. These pedicellariae are arranged regularly in pairs, the members of a pair being placed beside each other or slightly at an angle; the alveolae are spindle-shaped (about 1 to 1.5 mm long) with often a distinct constriction in the centre, the bevelled margin is smooth. The jaws of these pedicellariae are broad basally but taper to a narrow beak-like hyaline tip bearing one or several fine teeth; in general the blades are erect with the beaks meeting or over-lapping, when not erect the beaks probably lie flat in the narrow pointed tip of the alveolae. Towards the arm tips the blades of the pedicellariae are small and inconspicuous.

From two to eight distinct papulae occur between the members of a pair of pedicellariae; these are most numerous mid-way along the arm, becoming few and indistinct near the arm tip; these are also present between the pedicellariae of the disc and the marginal and actinal plates.

The madreporite (Fig. 2), nearer the edge than the centre of the disc, is almost oblong (about 2 mm by 1.5 mm), flat, finely dissected and almost completely surrounded by a naked fold of skin.

Centrally on the disc the anus is surrounded by about 12 distinct, large, irregularly shaped granules (Fig. 3).

Both series of marginal plates are well developed, from 35 to 36 extending from the base of the arm to the tip; distally the plates are oblong, proximally they are triangular or quadrate lying more or less opposite each other. Pedicellariae and papulae occur between the supero- and infero-marginal plates.

The actinal areas are distinctive (Fig. 4) with pedicellariae and papulae similar to those of the abactinal surface, except in the interradial regions where there are from five to seven pedicellariae with their long axis directed towards the interradial angle.

No granules occur on the furrow face of the adambulacral furrow spines; each adambulacral plate bears two round-tipped, upright furrow spines which form a sturdy palisade bordering the grooves. Proximally, each plate bears a single, sturdy, round-tipped, almost convex, usually sessile subambulacral spine page 4which lies at a slight angle to the furrow spine; distally these subambulacral spines are absent from every second plate, and near the arm tip they are even more indistinct, smaller and sometimes upright. Granules, similar to those found abactinally, occur between the subambulacral and furrow spines.

Within the narrow, deep ambulacral grooves the tube feet are biserially arranged with distinct sucking discs.

It is difficult to determine the exact limits of the oral plates; there are apparently four furrow spines similar to those of the adambulacral plates and one larger suboral spine similar to the subambulacrals.

Colour. In colour photographs of the living animal taken by Mr J. S. Bullivant the abactinal surface appears orange with darker chocolate-brown blotches, the whole being rather reminiscent of snakeskin. The actinal surface is similar, but the brown markings do not extend beyond the actinal papulae and pedicellariae; the adambulacral armature and mouth plates are orange.

Discussion. This new species is easily distinguished from the only other New Zealand species O. kermadecensis Benham, by the absence of granules between the adambulacral spines on the inner surface of the furrow; further differences occur in the arrangement and form of the pedicellariae. Although this new species is very distinct, it shows some affinities to O. lorioli Fisher and O. rhabdotus Fisher both from the Hawaiian Islands, however the present specimen differs from the former in the structure of the pedicellariae and in having only one madreporite, and from the latter in details of the adambulacral armature and in having the arms less distinctly fluted. It also shows similarities to the Torres Strait species, O. lioderma, but differs in having fewer papulae, a small terminal plate without tubercles and more regularly arranged pedicellariae, the blades of which vary considerably. This specimen is named for Mr D. G. MacKnight, who collected it.

Material Examined. 1 specimen from off East Cape; 37° 40ʹ S, 178° 56.4ʹ E (N.Z. Oceanographic Institute, Wellington, Station No. C 814), 112–84 fa.

Holotype. In the collection of the Oceanographic Institute, Wellington, N.Z. Holotype Number: 8.

R = 70 mm, r = 8 mm.