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Deep-Sea Echinoderms of New Zealand

Ophiuraster H. L. Clark, 1939

page 30

Ophiuraster H. L. Clark, 1939

A deep-sea genus established by H. L. Clark for a single species, O. perissus H.L.C. from off Aden, in 1,100 fathoms. It has not since been reported, and the species here referred to the genus is evidently new. The generic characters include:

The first lateral arm-plate enlarged, so as to meet its fellow of the adjoining arm, thus ringing the disc with a circle of radial and lateral plates, the disc not clearly demarcated from the arms. Oral shield small, lying proximal to the contiguous laterals. Tentacle-pores large, close together, near the ventral mid-line.

The structures which Clark (1939) called "radial shields" in his description of the type species are evidently the enlarged first lateral arm-plates, as can be inferred from his diagrams.

Ophiuraster symmetricus sp. nov. Plate 4, Figs. A, E, holotype.

Description: Disc circular in outline, with what appears to be a deep interradial notch; this notch, however, is really the space between the first lateral plates of adjoining arms. Aboral surface of the disc completely covered by scales, of which the imbricating primaries occupy the central region; beyond these lie the five pairs of polygonal radials, which are broadly contiguous. Interradially the radial shields are separated by a single prominent scale, and a few smaller scales are wedged between the primaries and the radial and interradial plates. The first pair of laterals make up the greater part of the oral surface of the disc, and also define the ambitus. The oral shields are small and transversely rhombic, distally wedged between the first laterals, proximally wedged between the adoral plates. The small adoral plates are broadly contiguous within, and separated without from the ventral plates by the large tentacle-pore, which carries three scales on its interradial margin. The oral plates each carry 6–7 oral papillae, in linear series, largest at the apex.

Arms: Upper arm-plates rhombic, declining rapidly distad, so that the distal arm-joints have none. The first upper arm-plate adjoins the radial shields and also the second upper arm-plate. The other upper arm-plates are widely separated. On the holotype there are only 7 upper arm-plates as against 10 lateral arm-plates. The lateral arm-plates are broadly contiguous above and below, except on the two basal joints. Each carries one larger and one smaller arm-spine, both arm-spines close together, conical in form, distally directed. The lower arm-plates are small; they vary in shape, and are nowhere contiguous. The basal tentaclepore carries 3 tentacle-scales, and others each carry one, relatively large, circular scale, attached to the corresponding lateral arm-plate.

Colour in Spirit: White.

Holotype: In the Dominion Museum, Wellington. R 5 mm, r 2 mm.

Material Examined: A single specimen, from 400 fathoms, NE of Mayor Island, Bay of Plenty, Dom. Mus. Station B.S.210, R. K. Dell, 28/2/1957.

Remarks: Ophiuraster symmetricus differs from O. perissus H. L. Clark in having three tentacle-scales on the basal arm-joint (instead of one only), in lacking the peripheral ring of plates within the ring of first lateral plates, and in its more regular arrangement of the aboral disc-scales. There is no "notch" at the interradial junction of the first laterals in O. perissus.

Attention may be drawn to the resemblance between Ophiuraster and Ophiomidas Koehler, both genera having the first lateral arm-plates similarly developed. The similarity extends also to the large, round tentacle-scales, the arm-spines and the adoral plates. The genera are easily distinguished by the first tentacle-pore, which is internal in Ophiomidas, external in Ophiuraster, differences which would lead to their classification, under Matusmoto's (1915) proposals, in the sub-families Ophiolepidinae and Ophiomastinae respectively. It would appear that Matsumoto's distinction of these two subfamilies is rather unnatural (though convenient) since it leads to the separation of forms which may well prove to be nearly related.