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Deep-Sea Echinoderms of New Zealand

Hippasteria Gray, 1840 — Hippasteria trojana sp. nov. Plate 1, Figs. A, G, holotype

Hippasteria Gray, 1840

Hippasteria trojana sp. nov. Plate 1, Figs. A, G, holotype.

Diagnosis: Large pentagonal body, defined by conspicuous, naked marginal plates, each of which carries one prominent conical spine, 35 or 36 marginals in the entire interbrachial arc from arm-tip to arm-tip. There may be one or two large bivalved pedicellariae on the more proximal superomarginals and inferomarginals, and exceptionally there may be two sub-equal spines instead of one. The abactinal plates carry a single erect conical spine or a large bivalved pedicellaria, and they are surrounded by smaller platelets or granules. Actinal area large, with numerous large bivalved pedicellariae, each surrounded by a circle of granules. The pedicellariae form a row parallel to each furrow margin, on the adjoining intermediate plates. Adambulacral armature comprising 3 robust furrow-spines, which are flattened distally, and 1 to 3 robust, erect subambulacral spines, the number depending upon the size of the adambulacral pedicellariae. Typical patterns are illustrated in Fig. A, which shows the 5th to 7th adambulacral plates of a ray of the holotype.

Material Examined: The unique holotype, taken at a depth of 220 fathoms on the Chatham Rise, at Station 6 of the Chatham Islands 1954 Expedition. The full description and photographic figures of this species will be given in the official report of that expedition.

Remarks: H. trojana resembles H. spinosa armata Fisher in having naked marginals armed with 1 or 2 spines and pedicellariae, but differs in having 3 furrowspines (as against a single one in H. spinosa armata), and 1–3 subambulacral spines (as against 1 only). From H. heathi and H. falklandica, both described by Fisher, the New Zealand form is at once distinguished by the marginal plates, which are inconspicuous and granulated in the two species named, and carry up to 5 spines. The species to which H. trojana appears most closely related is the one which is most remotely situated, in the Atlantic Ocean—namely, H. phrygiana (Parelius). Both species have conspicuous, naked marginals; H. phrygiana 2–3 furrow-spines, not unlike the condition in H. trojana. However, a specimen of H. phrygiana in my collection can be distinguished by its blunt, cylindrical furrow-spines, which are not at all flattened distally. H. phrygiana also tends to have more than one spine on each marginal plate, whereas this is exceptional in trojana. A still more striking difference is the complete absence of pedicellariae from the marginals in H. phrygiana. It does seem evident, though surprising, that the New Zealand species is closer to the Atlantic species than to the Pacific or Magellanic ones, and it may appropriately take the specific name trojana, the Phrygians and Trojans having been close allies (Iliad Bk. 2).

Although no living species of Hippasteria has hitherto been recorded from Australia or New Zealand, it is relevant to note that a fossil form, Hippasteria antiqua Fell, was described from upper Cretaceous sediments in Canterbury (Fell, 1956), only 600 miles west of the position in which the living species has been found. Hippasteria antiqua carries a single robust conical spine on each superomarginal. The condition of the adambulacrals and inferomarginals cannot be determined, but one obvious difference from H. trojana lies in the prominent carinal abactinal plates, lacking from the latter species.

Holotype: In the Canterbury Museum, Christchurch. Rays five, R 105 mm, r 62 mm.