Allostichaster Verrill, 1914

Allostichaster insignis (Farquhar, 1895)

• Stichaster insignis Farquhar, H. Trans. N.Z. Inst. 27, p. 203, Pl. 13 (1).

var. gymnoplax var. nov. Plate 2, Fig. C, holotype.

Diagnosis: Resembling Allostichaster insignis, but differing from the typical form in having the broad supermarginal plates almost completely naked. The only armature they carry is a tubercle at the upper end of the plate, and two or three small pedicellariae. The granulated surface of the superomarginals (diagnostic of Allostichaster) is thus exposed naturally. Three papulae form a triangle between the naked lower ends of adjoining plates. page 20The armature of the inferomarginals comprises two flattened spines. The adambulacrals are as usual diplacanthid, and occasional monacanthid actinal intermediate plates are seen. These features are all illustrated in the figure.

Material Examined: A single individual, R 35 mm, from 120 fathoms, off east Otago, edge of Canyon A, Dom. Mus. Station B.S.189, 14/8/1955, R. K. Dell. The holotype is in the Dominion Museum.

Remarks: The specimen has only five arms, instead of the usual six, and only one madreporite. These characters would have led me to conclude that it is not fissiparous, were it not for the fact that two rays are only half as long as the other three. It is probable that the animal has undergone fission, but has not yet reduplicated the madreporite in preparation for the next division. One further ground for caution before considering that the specimen represents a distinct species is the fact that Benham (1909) records a specimen of A. insignis from off Otago, having the spines "less numerous than in typical specimens"—without more exact details, unfortunately; he also received a specimen with only five arms and no madreporite. The evidence thus seems to favour extending the diagnosis of A. insignis to include gymnoplax as a varietal form. Should it later be found to be a well-defined form, the varietal name will be available for specific ranking.