“Amphiophiura gibbosa, n.sp.
St. 175. 2. iii. 27. Bransfield Strait, South Shetlands, 200 m. 3 specimens.
Diameter of disk of the largest specimen 6.5 mm., the arms rather stout, ca. 18 mm. in length, thus about three times the diameter of the disk. Disk covered by rather coarse scales, among which the polygonal central plate and five primary radial plates are conspicuous, particularly the latter, which form a wedge between the proximal ends of the radial shields.
These primary radial plates, together with the radial shields, are conspicuously elevated, and produce a somewhat gibbous appearance, recalling Ophiosteira Senouqui. The radial shields are contiguous in their distal half. In the younger specimens there is a single series of plates in the interradii, in the larger specimen several small plates have been added. No large plate on the edge of the interradii, also the ventral interradii are covered by small plates only, besides the buccal shields, which are fairly large, occupying about half of the interradius. In one case the proximal end of the buccal shield has been separated off as a small plate. Adoral and oral plates (jaws) of about equal size, in the main flat, simple. Mouth papillae usually three to each side of jaw, of the common type. First ventral plate triangular, conspicuously broader than the following ones, which are of the shape usual in this genus; the three or four proximal ones are contiguous. Dorsal arm plates contiguous in the proximal part of the arms, not much swollen. Arm spines three or four in the proximal part of arms, short, equidistant, none of them transformed into hooks. Arm comb well developed, but the papillae are short, not longer than the arm spines. Papillae along the genital slits rudimentary; the slits reach to the edge of the disk. Tentacle pores large, with numerous scales or papillae, as usual in the genus. Colour of preserved specimens whitish.
The species is viviparous. Probably it is also hermaphrodite, like A. Rowetti; but this I have been unable to ascertain definitely. Not thinking it desirable to spoil the type specimen, the only one preserved in alcohol, I have only opened one interradius from the ventral side, which showed merely the young embryos (with the skeleton just beginning to develop) lying as in A. Rowetti.
The character of the gibbous elevation of the primary radial plates and the radial shields distinguishes this species markedly from A. Rowetti, as well as from the other species of Amphiophiura known from the Antarctic seas or elsewhere. The species seems the nearest related to A. Rowetti, of which it may perhaps ultimately prove to be only a variety.”
(Mortensen, 1936; 342-343)
