Dermocoma, Hess, 1964

Thuy, Ben, 2013, Temporary expansion to shelf depths rather than an onshore-offshore trend: the shallow-water rise and demise of the modern deep-sea brittle star family Ophiacanthidae (Echinodermata: Ophiuroidea), European Journal of Taxonomy 48, pp. 1-242 : 159-160

Dermocoma sp. nov. innom. 4

Fig. 29 : 1

Material examined

NHM EE 14844 from the Tardefurcata Zone, early Albian of Leighton Buzzard, Great Britain.

Description

Dissociated, single, very large, proximal LAP; approximately twice higher than wide; dorsal and distal edges convex; ventral fifth of LAP strongly protruding ventro-proximalwards; proximal edge of LAP concave, with large central, swollen, protruding part not discernible as spur; outer surface with well-developed, regular vertical striation composed of fine, overlapping lamellae decreasing in size proximalwards; striation replaced by finely meshed stereom on proximal third of outer surface. Six moderately large, ear-shaped spine articulations in notches of weakly elevated distal portion of LAP; spine articulations equal-sized except for slightly smaller ventralmost one; weak dorsalward increase in size of gaps separating spine articulations; spine articulations proximally sharply bordered by edge of notches; ventral lobe of spine articulations with weak connection with distalwards projecting tip of outer surface stereom separating notches, and merged with dorsal lobe into continuous volute; gap between spine articulations and distal edge of LAP very narrow. Ventral edge of LAP with small, concave tentacle notch.

Inner side of LAP with moderately well-defined, prominent, very slender ridge with ventralwards pointing ventral part not merged with thickened ventral portion of LAP; dorsal part of ridge slightly bent, oblique, pointing dorso-proximalwards; ridge devoid of thickened parts and sharp kinks; inner side of distal edge with single, large, moderately well-defined, prominent, round spur; inner side of tentacle notch small, well defined laterally. Very shallow, poorly defined vertical furrow with small, scattered perforations dorsally bordering tentacle notch and distally bordered by narrow, moderately well-defined, weakly prominent ridge.

Remarks

The single LAP described here displays the distinctive combination of relatively small spine articulations in notches of the weakly elevated distal edge, with the strongly protruding ventral portion of the LAP and the simple, slender ridge on the inner side devoid of sharp kinks and thickened parts, which unambiguously places it in the genus Dermocoma . Within this genus, a number of species have up to six spine articulations but all of them display at least two spurs on the outer proximal and distal edge rather than a single, large, swollen, protruding area on the outer proximal edge and a moderately well-defined, round spur on the inner distal edge. This LAP clearly belongs to a new species, the formal description of which, however, should not be based on only a single specimen.

Figures

Fig. 29. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1. Dermocoma sp. nov. innom. 4 from the early Albian (Early Cretaceous) of Leighton Buzzard, Great Britain; NHM EE 14844, proximal LAP. 2-5. Dermacantha pattyana gen. et sp. nov. from the Hettangian (Early Jurassic) of Fontenoille, Belgium. 2. MnhnL HE414 (holotype), proximal LAP. 3. MnhnL HE415 (paratype), proximal LAP. 4. MnhnL HE416 (paratype), median LAP. 5. MnhnL HE417 (paratype), distal LAP. 6-8. Dermacantha seeweni (Kutscher & Hary, 1991) comb. nov. from the late Sinemurian (Early Jurassic) of Bishop’s Cleeve, Great Britain. 6. GZG.INV.78706, proximal LAP. 7. GZG.INV.78707, median LAP. 8. GZG.INV.78708, distal LAP. 9-11. Dermacantha leonorae gen. et sp. nov. from the early Pliensbachian (Early Jurassic) of Blockley, Great Britain. 9. GZG.INV.78710 (holotype), proximal LAP. 10. GZG.INV.78711 (paratype), median LAP. 11. GZG.INV.78712 (paratype), distal LAP. One common scale bar per species.