Asteroschema sampadae, Parameswaran, Usha V. & U, Abdul Jaleel K., 2012

Parameswaran, Usha V. & U, Abdul Jaleel K., 2012, Asteroschema sampadae (Ophiuroidea: Asteroschematinae), a new deep-sea brittle star from the continental slope off the southern tip of India, Zootaxa 3269, pp. 47-56 : 50-55

Asteroschema sampadae sp. nov.

Materials examined. Holotype and paratype [ CMLRE IO/SS/ECD/00021] collected on 20th May, 2007 from 454m (Lat. 7? 10’N Long. 77? 19’E) during FORV Sagar Sampada Cruise No. 254.

Diagnosis. Disc diameter (d.d.) about 18mm, arms about 380-450mm (21-23 times d.d.) Disc and arms covered by skin with small, scattered, distinctly conical epidermal ossicles on aboral side and minute spherical granular ossicles on oral side. Conical ossicles bearing a crown of minute spinous terminal projections. Dorsal ornamentation not closely packed anywhere on the body so that large parts of the disc and arms are overlaid by naked skin; but epidermal ossicles somewhat more dense on radial shields and at base of arms. Two arm spines from fourth arm segment; inner spine larger and approximately one third of the arm segment length, becoming twice the length of the arm segment in the middle of arm and bearing distinct thorny projections on the inner edge. The arm spines at the distal end of the arm are represented as small hook-shaped spines.

Etymology. The species is named after the vessel FORV Sagar Sampada, on which it was collected.

Type locality. Continental slope off the southern tip of India.

Description of holotype. Disc diameter 18.8 mm; arms between 380 mm and 450 mm long (about 21-23 times d. d.); moderately excavate inter-radially and covered by skin which bears conical epidermal ossicles aborally ( Fig. 2 B). Radial shields as narrow, elongate paired structures at base of arm; the shields widely separated running more or less parallel and extending a short distance beyond the disc proper; appearing to converge but not meeting centrally ( Fig. 2 B). Genital slits wide and vertical ( Fig. 2 C). Ossicles on aboral side of disc and around the genital slits are short and conical with a terminal projections at the tips ( Fig. 2 F); distributed more densely on radial shields than the rest of the disc, but not very closely packed anywhere, so that large parts of the disc and arms are overlaid by naked skin ( Fig. 2 A, B, D). Oral shield and oral plate covered by skin; embedded with minute spherical granular ossicles which are only visible when the dried skin is observed under a microscope. Oral plates elongate and extending into the mouth; bearing scattered, stout, domed granules on its vertical edge. Several, blunt and chisel shaped teeth; the lowermost tooth fragmented ( Fig. 2 C).

Arms not enlarged at the base; square in cross section, higher than wide at base (width 4.6 mm; height 4.9 mm); becoming more or less cylindrical and tapering distally. Aboral and lateral faces of the arm bearing conical epidermal ossicles similar to those on aboral side of the disc ( Fig. 2 D). Ossicles more numerous towards the base of the arms (2–3 granules in 1mm) and becoming scarce at the tip of the arms. They decrease in size towards the ventro-lateral margins; being represented on the oral side of the arm, as microscopic spherical granular ossicles, as on oral face of the disc ( Fig. 2 E).

Dorsal arm plates absent. Lateral arm plates small and ventro-lateral in position; the plates of each side meeting mid-ventrally, but not fused together. Tentacles of the basal arm joints covered by a hollow sheath which projects from the tentacle pore. Second tentacle pore without any arm spines, a single spine present in the next two arm segments and two spines thereafter. Arm spines bluntly tapering, covered by a thin layer of skin and bearing minute thorny projections on the inner edge ( Fig. 3 A, C, D). The inner arm spine always longer than the outer ( Fig. 3 A). Arm spines increase in size along the arm; at about a third of the arm length, the inner arm spine attains a length of 5mm (as long as the arm width and twice as long as the arm joint), becoming distinctly cylindrical with welldefined thorny projections on the inner edge ( Fig. 3 C, E). A mass of soft tissue adheres to the terminal projections, making the spine appear club-shaped ( Fig. 3 A). The outer one reaching a maximum length of about 3 mm and remaining bluntly tapering ( Fig. 2 D, F). Towards the distal third of the arm, both spines become progressively smaller and are represented as hooks, which do not have a lamina or regularly arranged perforations ( Fig. 3 B, G).

Colour in life, fawn; the disc relatively darker than arms with a greyish tinge; skin over the ossicles, tube-feet and tips of arm spines dark brown. Disc greyish and arms pale wheat in preserved specimen.

Description of paratype. Disc diameter 17.6 mm; arms about 19–22 times d. d., arm width at base 4.2mm, height 5.2 mm. Disc is slightly more excavate than the holotype, with the central part of the disc a bit concave. This difference is likely to be because the mouth of the paratype is gaping open. Similar to holotype in all other characters.

Biological association. Asteroschema sampadae was found in association with a gorgonacean of the family Primnoidae .

Comparisons. Asteroschema sampadae resembles A. oligactes ( Pallas, 1788) and A. tumidum Lyman, 1879 in the shape of the epidermal ossicles of the aboral side, but differs in the distribution of these ossicles, which is regular and close-set in these species but rather irregular and scattered in A. sampadae . The inner arm spines of A. oligactes is not much longer than the outer, whereas the inner arm spines of A. sampadae become twice as long as the outer towards the middle of the arm. In A. tumidum , the inner spine attains a length equaling one-third of the arm segment (2mm) and becomes rough ended and clubbed. While the shape of the inner spine of A. sampadae is similar to that of A. tumidum , the spines of A. sampadae are much longer, attaining twice the length of an arm segment (5mm). Moreover, A. sampadae is much larger than the type specimen of A. tumidum (8mm d. d., arms upto 135mm).

While the minute granular epidermal ossicles on the oral side of A. sampadae are similar to those of A. flosculus Alcock, 1893 and A. nuttingii Verrill, 1899 , the ossicles on the aboral side of these two species are closeset granular ossicles unlike A. sampadae . The arm spines of A. sampadae are similar in description to those of A. nuttingii , in which the inner spine is longest and largest, cylindrical and blunt, enlarged at the end with minute projections at the tip. A. nuttingii is the only other species to be described as having claw-like distal arm spines.

A. sampadae is similar to A. tubiferum Matsumoto, 1915 with respect to the maximum size attained by the inner arm spines as well as the presence of a sheath around the basal tentacles. However, A. tubiferum possesses only coarse granular epidermal ossicles on the aboral side, while the aboral ossicles of A. sampadae are all distinctly conical. A. hemigymnum Matsumoto, 1915 also possesses a sheath around the basal tentacles, but the aboral ossicles of this species are close-set, fine, smooth granular ossicles, unlike the spaced conical ossicles of A. sampadae .

A. sampadae differs greatly from A. lissum H. L. Clark, 1939 which has been reported from the nearby Maldives region, in its size as well as the shape of epidermal ossicles; A. lissum (8mm d.d., arms about 110mm) possesses only close-set, fine, low granular ossicles (40–60 in 1mm) on the aboral side. While both A. fastosum Koehler, 1904 and A. subfastosum Döderlein, 1930 have conical ossicles embedded in the aboral skin, A. sampadae differs from both in the nature of ossicles on the oral side, which are small, flattened conical ossicles in A. fastosum and close-set, smooth, hemispherical granular ossicles on A. subfastosum . In addition, the arm base of A. fastosum is distinctly enlarged, while that of A. sampadae is not. A comparison of A. sampadae with all species of Asteroschema having conical as well as granular epidermal ossicles, based on literature is presented in Table 2.

Some species of the genus Ophiocreas Lyman, 1879 also have epidermal ossicles of various kinds and of these, Ophiocreas spinulosus Lyman, 1883 bears prominent blunt ‘spines’ or conical ossicles on the aboral skin. However, these are restricted to the radial shields and arm bases in O. sibogae , whereupon they are distributed evenly—a pair to each arm joint; while in the case of A. sampadae , the ossicles are irregularly scattered all over the aboral side of the disc and arms.

Remarks. The most distinctive features of A. sampadae which separates it from other species are the shape and nature of the epidermal ossicles on the aboral and oral sides along with the large inner arm spines in the middle of the arms that are represented as hook-shaped structures at the distal part of the arm. The characteristic shape of the conical epidermal ossicles of the aboral side, crowned with short terminal projections is of significance.

Figures

FIGURE 2. Asteroschema sampadae sp. nov., A – C. live specimens, D – F. Holotype (CMLRE IO / SS / ECD / 00021). A. entire organism, B. aboral view of disc, C. oral side of disc showing genital slits (arrow), D. holotype (CMLRE) conical epidermal ossicles on the aboral side of the arm (arrows), E. oral side of arm base, showing minute granular epidermal ossicles (arrow), F. conical epidermal ossicle from the aboral side of the arm, with terminal projections (arrow).

FIGURE 3. Asteroschema sampadae sp. nov., holotype (CMLRE IO / SS / ECD / 00021). A. arm in lateral view, middle of arm showing arm spines (left = dorsal, right = ventral), B. arm in lateral view, distal end of arm (left = dorsal, right = ventral), C. inner arm spine from middle of arm, showing terminal projections on inner edge (arrow), D. outer arm spine from middle of arm, showing terminal projections on inner edge (arrow), E. SEM image of tip of inner arm spine from middle of arm, F. SEM image of outer arm spine from middle of arm spine, G. hook-shaped arm spine from distal end of arm. Abbreviations: IS, inner arm spine; OS, outer arm spine; HS, hooked spines.