Asterodiscides bicornutus, Lane & Rowe, 2009

Lane, David J. W. & Rowe, Frank W. E., 2009, A new species of Asterodiscides (Echinodermata, Asteroidea, Asterodiscididae) from the tropical southwest Pacific, and the biogeography of the genus revisited, Zoosystema 31 (3), pp. 419-429 : 421-425

publication ID	https://doi.org/ 10.5252/z2009n3a2
persistent identifier	https://treatment.plazi.org/id/1E3F2117-FFF4-FF99-FF76-FD45FC1D025D
treatment provided by	Marcus
scientific name	Asterodiscides bicornutus
status	sp. nov.

Treatment

Asterodiscides bicornutus View in CoL n. sp.

( Figs 1-3 View FIG View FIG )

HOLOTYPE. — Vanuatu. SANTO 2006 Expedition, stn AT076, Espiritu Santo, NW Malo Island , from RV Alis trawl, near Wombwanavua Point, 15°38’01.14”S, 167° 04’46.20”E- 15°38’40.26”S, 167°03’38.28”E, depth 105-135m, 10.X.2006, collected and photographed alive by first author ( MNHN IE.2009.4909). GoogleMaps

DIAGNOSIS. — Large (R = 102mm) stellate 5-armed asteroid, R/r = 1.7, arms and disc thick (25 mm after preservation), abactinal surface densely covered with stout, conical, pointed spines, some being bicornute or T-shaped with the two points extending to form a spindle shape arising directly from the spine base. Superomarginal plates 4, the terminal ovate or tear-shaped pair being large and conspicuous, the other 3 being small, inconspicuous and located proximally. Inferomarginal plates 6-7, adambulacral furrow spines 6-7 per plate, subambulacral spines in double row.

ETYMOLOGY. — Species name “bicornutus” derived from the Latin “cornu” for horn and referring to the two-horned, T-shaped abactinal spines.

DESCRIPTION

The single specimen, the holotype, is stellate ( Fig. 1A View FIG ); R/r = 102/ 60 mm. Upper surface of disc and arms convex in profile, flattening after preservation, lower surface flattened but curved upwards toward the arm tip. Rounded madreporite is 4 mm in diameter and located 30% of the interradial distance r from the anus. Abactinal armament of conical, bluntly pointed spines 4-8 mm in length, small rounded tubercles, and granules. In addition, some of the conical spines, which are oriented more horizontally than vertically, have a bulging basal expansion. These are transitional to bicornute spines where the basal expansion is drawn out into a conical point equal or subequal in size and opposite in direction to that of the main conical axis ( Figs 1B, F View FIG ; 2B). Bicornute spines have a sessile T-shaped appearance and are distributed as follows: absent from central disc; along the surface of each arm to the arm apex forming a more or less distinct carinal row and two lateral rows ( Fig. 3 View FIG ), often alternating with one, or sometimes two, normal conical spines; also present dorsolaterally and laterally but their distribution is more irregular. Length of bicornute spines, from tip to tip, 8-12 mm. Most spines are encircled at their base by a ring of granules. Papulae are densely but irregularly distributed on the abactinal surface

Actinal surface flattened and covered with a cobblestone-like armament of rounded tubercle clusters, or single rounded tubercles, on each plate ( Fig. 1C, E View FIG ) with smaller angular granules between the tubercles. Tubercle components in each cluster from 2-6 per plate and have flat surfaces where they adjoin and fit together. Distally the actinal tubercles are single and towards the arm tip they show a transition to short, blunt, conical spines ( Fig. 1D View FIG ). Adambulacral plates 50-53 with comb-like arrays of 6 or 7 furrow spines per plate ( Fig. 1D View FIG ). Subambulacral spines in a double series, short, round-ended and tend to be flattened transversly ( Figs 1D View FIG ; 2A). Spines of the outermost subambulacral row, furthest from the ambulacral groove, decrease in size distally near the arm apex ( Fig. 1D View FIG ); approaching the oral region they diminish in size followed by one or two enlarged ones, before diminishing again near the mouth. Spines of the innermost row of subambulacrals become slightly elongated and more cylindrical distally (Fig. 2A), where the arm furrow is curved upwards, before diminishing in size towards the arm tip. Most of the spines in the proximal half of the innermost subambulacral row are split transversely or obliquely, forming doublet pairs, then towards the mouth they become single, robust and prismatic in section, eventually diminishing in size near the mouth.

FIG. 2. — Asterodiscides bicornutus n. sp., holotype, alcohol preserved specimen; A, ventro-lateral view of arm showing the positions of the six inferomarginal plates (black arrows) and the three proximally located superomarginal plates (white arrows), the white block arrow indicates where a spine has become detached, showing a ring of granules at the spine base; B, dorsal view of re-curved arm apex showing the large pair of tear-shaped, terminal superomarginals (*). Many of the abactinal spines are bicornute.

Marginal plates do not form a contiguous series but are widely separated.Superomarginals comprise three small proximal plates and one prominent, terminal plate on each side of each arm. Each plate is encircled by a ring of granules.Proximal superomarginals (Fig. 2A, white arrows) are rounded or somewhat irregular in shape. The large, ovate-elongate, terminal superomarginals are convex in profile; they taper distally, with the narrow ends of each pair almost meeting, close to the terminal plate of the ambulacral groove (Fig. 2B). Inferomarginal plates, numbering 6-7 (Fig. 2A, black arrows), are similar in size to many of the nearby actinal tubercles but are distinguished by their flatter appearance.

Pedicellariae are numerous and found on abactinal, actinal, superomarginal, inferomarginal and, infrequently, adambulacral plates. They are forcepsshaped and located at the base of spines or tubercles ( Fig. 1F View FIG , arrows). Each jaw is tapered and U-shaped in section with flat faces apposed to each other when in the closed position. The pair of jaws is often curved laterally to fit the curvature of the spine base or tubercle.

Colour in life

Body wall of disc and arms a yellow sandy hue on upper and lateral surfaces. Colour of many spines and tubercles ranges from orange-red to pale pink with the orange-red pigmented spines forming a well-defined circular area centrally on the disc, then more diffuse areas peripherally towards the ends of the arms.Other spines and tubercles located between, or sometimes within, the orange-red zones are cream or pale pink ( Fig. 1A, B, F View FIG ). The large terminal superomarginal plates are orange to pink. Abactinal papulae are reddish. Actinal surface is sandy yellow to pale cream with broad, orange-yellow streaking along interradial zones and parallel but irregular minor streaks of the same colour at intervals along the arms ( Fig. 1C View FIG ).

REMARKS

Asterodiscides bicornutus View in CoL n. sp. is most closely related to Asterodiscides grayi Rowe, 1977 View in CoL in that 21 of the 22 morphological characters derived from the first 16 character sets for A. grayi View in CoL in Rowe’s (1985) original character matrix match those for the new species described here (also see phenetic analysis below). Characters 17 and 18 of Rowe (1985) are omitted from the present analysis due to ambiguity or deficiency in data. Additionally, forceps-shaped pedicellariae, present on abactinal, actinal, superomarginal and inferomarginal plates in A. grayi ( Rowe 1977) View in CoL are present also in A.bicornutus View in CoL . Oguro (1991), in describing A. japonicus View in CoL from Japan, extends Rowe’s 1985 character matrix to include pedicellariae for the genus but he does not include the information on pedicellariae noted in Rowe’s account (1977) for A. grayi View in CoL . A striking difference between A. bicornutus View in CoL n. sp. and A. grayi View in CoL is the presence in the former of bicornute pointed abactinal spines ( Table 1, attribute 23). These T-shaped bicornute spines distinguish this specimen not only from A. grayi View in CoL but also from any known species in the genus. Conical abactinal spines in A. grayi View in CoL , all of them with single apices, occur in three size ranges ( Rowe 1977), the largest forming carinal and lateral rows that are similar in disposition to the rows of bicornute spines described here. Bicornute spines are however considered to be sufficiently distinctive to merit the designation of a new Asterodiscides species.