Ophiomoeris exuta, Stöhr, Sabine, 2011

Stöhr, Sabine, 2011, New records and new species of Ophiuroidea (Echinodermata) from Lifou, Loyalty Islands, New Caledonia, Zootaxa 3089, pp. 1-50 : 21-23

Ophiomoeris exuta sp. nov.

Figure 8A, B , 9

Type material. Holotype, on SEM stub, sta. CP1646, off Cap des Pins, 21°02.6'S, 167°31.6'E, 420–480 m [ MNHN IE- 2009-9207]; 4 paratypes, in 80% ethanol, type locality [SMNH-Type-8077]

Etymology. The specific name is derived from the Latin word for bared, alluding to the naked interradial disk.

Holotype description. Disk lobed, interradially incised, dd 3.0 mm (prior to SEM preparation); five curled arms. Not attached to coral (although probably dislodged). Radial shields much longer than wide, narrow, with convex outer and straight inner edge; pairs contiguous over almost entire length, except at distal end, where a small fan-shaped dorsal arm plate separates them. Single round scales of variable size, bearing conical granules, lay on top of the radial shields, but do not separate them. Centre of disk with large round centrodorsal plate, larger round plates bearing small conical granules (presumably the radial primary plates), interspersed with smaller scales lacking granules. Dorsal interradial disk consists of naked skin. Arms noded, dorsal arm plates small, rounded triangular to fan-shaped, about 1.5 times as wide as long, widely separated by the lateral plates. Six conical arm spines on arm base, dorsalmost longest, longer than an arm segment, spines decreasing in size ventralwards. Spines on proximal arm smooth, distally with fine teeth at ventral edge and terminal tooth, slightly hook-shaped.

Ventral disk naked skin, jaws with pointed apical papilla similar to teeth, three spiniform lateral papillae. Large adoral shields with angled abradial edge, concave adradial edge, pairs meeting over half their abradial edges, not separating the oral shield from the arm. Oral shield smaller than an adoral shield, fan-shaped, wider than long, with proximal point, concave lateral and convex distal edges. First ventral arm plate integrated into oral frame, longer than wide, strongly convex lateral edges. Second ventral arm plate twice as wide as long, trapeziform with wider proximal edge, fragmented on two arms. Following ventral arm plates reduced to small, round, thin scales, embedded in a strand of thick skin running along the entire arm. A single oval tentacle scale at each pore. The stereom structure of all plates is glass bead-like.

Bursal slits half as long as interradial ventral disk, lined with long adradial genital plate and several scales on abradial edge.

Colouration in ethanol cream with brown longitudinal line on dorsal arms and midline of radial shield pairs.

Paratype variations. Disk diameters of four paratypes are 1.6 mm, 2.4 mm, 3.2 mm, and 3.5 mm. All are attached to various species of coral. Some lack granules on the dorsal disk, others have fewer than the holotype or just tumid scales. The size of the scales overlaying the radial shields varies between individuals, as does the number of central dorsal scales. Smaller specimens have fewer arm spines than the holotype, none has more than six.

Remarks. The arrangement of the oral frame, the glass bead-like structure of the stereom, the lobe-like shape of the disk all concur with Ophiomoeris , a genus that has until recently been placed in Hemieuryalidae . The arm spine articulations of the new species concur with that shown for Ophiochondrus by Martynov (2010a), interpreted as a variation of the for Ophiacanthidae typical comma-shape ( Paterson 1985; Martynov 2010b). In combination with the spiniform oral papillae, the shape of adoral and oral shields, and the long arm spines that turn into hooks, a placement within Ophiacanthidae seems indeed more appropriate. The large naked radial shields and deeply incised disk are characters of Paterson's (1985) subfamily Ophioplinthacinae . There is some similarity in the radial shields with Ophiohamus , but that genus has a round flat disk and specialized arm hooks. Previously, three species of Ophiomoeris were recognized (see below), but none of them has a naked disk. The naked disk interradii, both dorsally and ventrally, are an unusual feature among hemieuryalids as well as ophiacanthids, which separates the new species from all others. Also, the long, narrow and contiguous radial shields differ from all other species of Ophiomoeris .

Distribution. Known only from the type locality.

FIGURE 9. SEM images of Ophiomoeris exuta sp. nov. holotype MNHN IE-2009-9207. A, dorsal aspect, note the naked interradials; B, dorsal arm; C, distal arm laterally, note the hook-shaped spines; D, oral frame; E, arm spine articulation; F, ventral arm; G, ventral interradius, naked except for genital plates. Scale bars in millimetre.

Figures

FIGURE 8. A, B, Ophiomoeris exuta sp. nov., holotype MNHN IE- 2009 - 9207, prior to SEM preparation; A, dorsal aspect; B, oral frame and ventral arm. C – E, Ophiomoeris cf. obstricta; C, dorsal aspect; D, jaw details; E, dorsal arm. F, Ophiomitrella granulosa, spotted form, dorsal aspect. Scale bars 1 mm.