Comprehensive DescriptionRead full entry
“CLADASTER MACROBRACHIUS * sp. nov.
R = 40 mm.; r = 10 mm.; R, = 2.5r; br = 18 mm. but at halfway to tip it is only 9 mm. Disk large, somewhat convex but only about 8 mm. thick, even at center. . Rays flat, tapering, at first rapidly, then gradually to the blunt tip. Abactinal plates moderate in both size and number, irregularly polygonal, with rounded corners, thick and close together; papulae few, single, typically six about any one plate on center of disk or base of rays but usually one or more of the six, lacking. Each plate, in life, was evidently surrounded by a marginal series of small, well spaced granules and bore on top, several larger, more widely spaced granules, one of which was here and there replaced by a large bivalved, more or less excavate pedicellaria; in the preserved specimen (dry) all the top granules, some pedicellariae and many marginal granules have been rubbed off but each has left a shallow pit to indicate its location. Median radial series of plates shut off from terminal plate by the meeting of the five distal pairs of superomarginals; series of plates adjoining radials only extends as far as the fourth or barely to the fifth superomarginal. Madreporite small (less than 2 mm. in diameter), pentagonal, situated about 10 mm. from the disk margin. Superomarginals 13 or 14 on each side of each ray, wider than long, more or less markedly tumid; like the abactinal plates, each is surrounded by a marginal series of small granules, and in life was very sparsely covered by much coarser and more widely spaced granules; on the upper end of each plate, where it is most markedly tumid, there are two or three (distally one or none) large, shallow scars, which indicate that in life rather coarse granules or big tubercles were present. Terminal plate small and swollen; there are indications that in life it may bear 1-3 tubercles. Inferomarginals agreeing with superomarginals in number, form, size, position and granulation, except that the large, shallow scars are as a rule less well-marked and often seem to be wanting. Actinal plates few, irregularly arranged (except for series adjoining adambulacrals), of diverse sizes; the smaller ones are pretty well covered by the very large marginal granules, but all the larger plates show a bare central area on which is a big, wide-valved pedicellaria, and rarely a single big granule also; the series adjoining adambulacrals extends out only as far as the fourth inferomarginal.
Adambulacral armature conspicuously heavy; the plates themselves are numerous, about 45 in each series, crowded, much wider than long proximally, but squarish distally; each plate carries a series of 3 (rarely 2) furrow spines, about a millimeter long near middle of arm (longer proximally, shorter distally) subequal, or middle one longest, markedly compressed at right angles to furrow and more or less conspicuously widened at tip; back of these is a second series of which the adoral is very small, the middle one is much larger and the aboral is a stout, somewhat capitate subambulacral spine, the largest spine on the plate; on the outer margin of the plate is a third series of three spines of which the middle one is much the largest; the two small ones are hardly bigger than the marginal granules of the adjoining actinal plates; proximally all the adambulacral spines are longer, heavier and more conspicuous, while distally they decrease in number as well as in size. Oral plates not swollen, their outlines hard to determine; each has a marginal series of strongly compressed spines, about 2 mm. long, with much widened tips; there is also a series along the sutural margin consisting of 5 or 6 spines of which the first is small and pointed, the second is a long heavy spine like those of the free margin, the third is like it but a little smaller and the remainder are successively shorter and smaller in every way. Color of dried specimen, light yellowish-brown.
P.F. 2798. Vasco de Gama Peak, N. 71° E., 18 miles. 230 fms. Stones 1 specimen; adult?
P.F. 17998. Cape Point, N.E. ¾, N., 39 miles, 310-500 fms. Gn.m. 1 specimen; adult?
Holotype, South African Museum, no. A 6429, P.F. 17998.
Aside from these interesting individuals, which differ little from each other, only two specimens of Cladaster are known; one, the holotype of C. validus Fisher with R = 17 mm. was taken near the Aleutian Islands; the other, the type of C. rudis Verrill with R = 25 mm., in the West Indies. The present individuals are thus much larger and it is noticeable that they have clearly the longest arms; C. validus is most nearly pentagonal. Probably the relative length of the rays increases with age. Perhaps the number of spines in the furrow series also increases with age, for the South African form has three as against two in the other species. Whether these South African specimens are adult seems doubtful and it is probable that a fully grown specimen would throw much light on the relationships of the genus. If it is true that the superomarginal plates in macrobrachius bear coarse tubercles, the definition of the genus will need some modification.
*μαχρός = long + βραχίων = arm, in reference to the relatively long rays.”
(Clark, 1923: 268-270)