“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)
Labidiaster annulatus, the Antarctic sun starfish or wolftrap starfish is a species of starfish in the family Heliasteridae. It is found in the cold waters around Antarctica and has a large number of slender, flexible rays.
Labidiaster annulatus has a wide central disc and 40 to 45 long narrow rays and can reach a diameter of 60 centimetres (24 in).[2] The disc is slightly inflated and is raised above the base of the rays. The madreporite is large and near the edge of the disc. The aboral or upper surface is covered in a meshed network of small slightly overlapping plates. These are covered by a membrane with numerous raised projections called papulae, some small spines and a few large triangular pedicellariae, wrench-like organs that can grasp objects. The rays are crowded together where they join the disc and their aboral surface is similarly clad in overlapping scales in a quadrangular mesh pattern. There are also short spines and many papulae and a number of small pedicellariae. At intervals down each ray there are transverse bands armed with numerous large pedicellariae. The oral or lower surface of the disc has a central mouth surrounded by further scales. The ambulacral grooves are wide and run down the centre of the oral side of each ray. There are widely separated narrow scales on either side of the grooves with two spines on each, one overlapping the groove and the other projecting from the side of the ray. There are rows of tube feet on either side of the groove, each foot having a button-like suction pad at the tip.[3]
Labidiaster annulatus is found around the Antarctic Peninsula, South Georgia and the South Sandwich Islands. The depth range is from the intertidal zone down to 554 metres (1,818 ft) but this starfish most commonly occurs between 30 and 400 metres (98 and 1,312 ft). It lives on the seabed and is found on sand, mud and gravel and among rocks.[4]
Labidiaster annulatus is an opportunistic predator and scavenger. It moves about on the seabed using various combinations of rays. It often climbs to an elevated position on top of a rock or a large sponge. Here it holds on with some of its rays while it extends others like fishing rods.[4] The rays are long and flexible and writhe about in search of prey. Invertebrates or even small fish that come in contact with the extended rays are grasped by the pedicellariae which snap shut. Other rays then curl around the struggling prey. It is manipulated to the underside of the rays where it is passed along by the tube feet to the mouth. This is extensible and can ingest large items. The prey continues to struggle while it is being transported and may escape. Analysis of stomach contents showed that krill and amphipods were the most frequent diet items. Sediment was also often present and may have contained microflora such as of foraminiferans. A portion of a fish measuring 6 centimetres (2.4 in) was found in one individual but it was unclear whether it had been caught alive or had been scavenged. Other dietary items were varied and included smaller starfish of this species and brittle stars such as Ophionotus victoriae.[4]
Little is known of the reproduction of Labidiaster annulatus, but the larvae pass through at least one bipinnaria and one brachiolaria stage as has been demonstrated by DNA analysis. The larvae are planktonic and spend many months drifting with the currents before settling on the seabed and undergoing metamorphosis into juveniles.[5]
Labidiaster annulatus, the Antarctic sun starfish or wolftrap starfish is a species of starfish in the family Heliasteridae. It is found in the cold waters around Antarctica and has a large number of slender, flexible rays.
