“RETASTER GIBBER, n. sp.
Marginal contour substellate, interradial angles acute, not rounded. Minor radial proportion about 50 per cent.; R= 28 millim., r=14 millim. Radii 5, well rounded, tapering continuously from the angle to the extremity, with sides rounded, tumid, and curving over on to the actinal area as in Echinaster. Dorsal profile high, gibbous, rounded. On the actinal area the mouth and surrounding portions are deeply sunken.
Supradorsal membrane with reticulated fibrous bands, marking it off into square or rhomboid meshes of great regularity. In the centre of each, 3 to 4 paxillae-spinelet-tips are visible; and other spinelets radiate to the mesh-fibres, one (or occasionally
two) spiracula being situated in the interspaces. The white fibres of the meshes form a conspicuous feature; and the slightly protrusive tips of the spinelets impart a granulose appearance to the dorsal area, the whole being covered with a thin fleshy membrane. The oscular orifice is small, closed by a number of sub-papillate spinelets, rather longer, more prominent, and more robust than those of the paxillae proper.
Ambulacral furrows narrow and deeply sunken. Ambulacral combs quite within the furrow and below the level of the test, with 3 to 5 spinelets, which are short, rather robust, webbed together,—the membrane being very slightly indented and with a slight knob over the end of each spinelet. Ambulacral suckers completely hidden by the overarching combs.
Mouth-plates deeply sunken; mouth-spines longer than the ambulacral spines, 3 on each plate, the whole six being webbed together into a continuous comb. Each plate bears one large isolated secondary or superficial spine, longer than the mouth-spines, very robust, covered with a thick membrane, except at the tip, which is translucent and sharply pointed.
Segmental apertures elongate and narrow; papillae free on the aboral side only.
Actino-lateral spines very short and robust, almost hidden within the furrow, of which they appear to form the sides, and only protrude a short way beyond the level of the test, standing nearly perpendicular to the plane of the ray, and in some parts showing a tendency even to arch over the furrow slightly. This disposition, together with the aborted character of the fringe, imparts a feature very different from that usually presented by this structure in Pterasteridae. In the immediate angle, near the peristome, the actino-lateral spines are somewhat longer, and are laid over upon the rounded surface of the interbrachial area, their web being continuous and forming a smooth fleshy triangular area leading up to the mouth-angle.
Colour, in alcohol, yellowish or greyish white.
Station 311. Lat. 52°50' S., long. 73°53' W. Depth 245 fms.; bottom temperature 7.7° C.; mud.”
(Sladen, 1882: 200-201)
