Comprehensive DescriptionRead full entry
“Labidiaster annulatus, n. sp. (Pl. CVIII. fig. 1).
Rays forty to forty-five. R = 165 to 190 mm.; r = 33 mm. R > 5 r. Breadth of a ray at about 20 mm. from the disk, 6 to 7 mm.
Rays elongate, delicate, and cylindrical; constricted at the base, where they are closely crushed together, then gradually swelling slightly, the ray being broadest at about the end of the inner third or fourth, beyond which it gradually tapers to an attenuate extremity. The interbrachial arcs are a mere close cleft, in consequence of the crowding of the rays at the base.
The disk is large and circular, subplane, and capable of slight inflation, slightly elevated above the base of the rays, and more or less distinctly defined. The abactinal surface is beset with small imbricating plates forming a wide meshed network, the whole being covered with a membrane which is punctured interspaces by numerous papulae. The plates bear small uniform spinelets, scarcely, if at all, larger than those upon the rays, and here and there, widely spaced, are large, triangular, forficiform pedicellariae; much smaller, elongate, forficiform pedicellariae are more numerous.
The abactinal surface of the ray on the basal portion is similarly beset with small imbricating plates, which form a wide meshed network, the meshes being more or less quadrangular. The longitudinally directed series of plates are, however, confined strictly to the abactinal surface, and do not occur on the lateral walls of the ray, where widely spaced, transverse series only are found, one opposite about every third adambulacral plate. The lowest plate, which abuts on the adambulacral plates, is probably the representative of an infero-marginal plate, and bears a single small, sharply pointed spinelet. The abactinal plates do not extend far beyond the ovarial region of the ray, and the transverse bands fire then probably represented only by an aborted rudiment of the infero-marginal plate, bearing, however, a fully developed spine, which may extend for two-thirds of the length of the ray or more. The abactinal plates bear small, isolated, sharply pointed spinelets, similar to those upon the disk, and the membrane which covers the interspaces is punctured by numerous papulae. A number of small forficiform pedicellariae occur on the membrane, and great numbers of comparatively large forcipiform pedicellariae are present, borne on a roll or sacculus of membrane, and disposed as a thick transverse ruff or annulus, isolated and well spaced from its neighbours, encircling the ray, and extending on each side to the adambulacral plates.
The ambulacral furrow occupies the greater part of the actinal surface of the ray, measuring about 4 mm. at a part where the whole ray is 6.25 mm. The adambulacral plates are short and narrow, inclined at a considerable angle aborally, and are separated by a space nearly equal to their length occupied by muscular ligament. Their armature consists of two short, cylindrical, tapering, sharply pointed spines, which diverge slightly, one towards the furrow, the other outwardly. The bases of the two spinelets together occupy the whole of the actinal surface of the small adambulacral plates. On the outer side of the outer spine is a rather elongate tuft of small forcipiform pedicellariae, and within the margin of the furrow and at the base of the inner spine may be one or occasionally two very small forficiform pedicellariae. The ambulacral tube-feet, which are robust and crowded, are biserial in their arrangement, and have a small, button-like, centrally invaginated terminal disk.
The actinostome is large and wide, its diameter being about 38 mm. in the specimen described. The buccal membrane, which is of broad expanse, is thick and leathery, and is marked with very fine radiating lines of low, crowded, villiform papillae.
The madreporiform body is large and prominent, often slightly elevated above the general surface of the disk, and is situated close to the margin. Its outline is irregularly circular, 7.25 mm. in diameter, and is surrounded by a series of closely placed, small, pointed spinelets, about forty-five in number. Its surface is marked with very fine, much convoluted striations, which show a regular centrifugal radiation on the outer part.
Colour in alcohol, a dirty ashy grey.
Localities.—Station 149H. Off Cumberland Bay, Kerguelen Island. January 29, 1874. Depth 127 fathoms. Volcanic mud.
Station 150. Between Kerguelen Island and Heard Island. February 2, 1874. Lat. 52° 4' 0" S., long. 71° 22' 0" E. Depth 150 fathoms. Coarse gravel. Bottom temperature 35.2° Fahr.; surface temperature 37.5° Fahr.
Station 151. Off Heard Island. February 7, 1874. Lat. 52° 59' 30" S., long. 73° 33' 30" E. Depth 75 fathoms. Volcanic mud. Surface temperature 36.2° Fahr.
Station 191. In the Arafura Sea, north-west of the Arrou Islands. September 23, 1874. Lat. 5° 41' 0" S., long. 134° 4' 30" E. Depth 800 fathoms. Green mud. Bottom temperature 39.5° Fahr.; surface temperature 82.2° Fahr.
Remarks.—This species may be distinguished from its near ally, Labidiaster radiosus, by the more numerous and comparatively more slender rays, by the uniformity in the size of the spinelets on the disk and at the base of the rays, and by the tufts of forcipiform pedicellariae upon the rays forming a thicker and more complete annulus. Although the verbal account of these differences may lead to the inference that they are comparatively insignificant, they produce a very distinct facies, as may be seen on referring to Pl. CVIII. I am unable to detect any difference worthy of note between a small example from Station 191 and those from the neighbourhood of Kerguelen and Heard Islands. I have previously drawn attention to the remarkable occurrence of Antarctic forms at this station.”
(Sladen, 1889: 595-597)