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 : 140

Dermocoma sp. nov. innom. 1

Fig. 25 : 6

Material examined

GZG.INV.78674 from the Rhaetian of Fischerwiese, Austria.

Description

Single, dissociated, moderately large, median LAP known; nearly as high as wide; dorsal edge slightly concave as a result of a constriction; distal edge convex; ventral sixth of LAP protruding ventroproximalwards; proximal edge irregularly undulose, with two medium-sized, very poorly defined, weakly prominent but protruding spurs, one in the middle of the dorsal half, the other in the middle of the ventral half; outer surface with rather coarse, poorly developed vertical striation composed of broad, slightly overlapping lamellae close to spine articulations, replaced by finely meshed stereom on proximal half of outer surface. Four large, ear-shaped spine articulations in moderately deep notches of elevated distal edge of LAP; ventral and dorsal lobes merged into continuous volute; ventral lobe not connected with outer surface; spine articulations proximally sharply bordered by edge of notches; spine articulations nearly of equal size except for slightly smaller ventralmost one; very weak dorsalward increase in size of gaps separating spine articulations. Ventral edge of LAP with moderately large, concave tentacle notch.

Inner side of LAP with moderately large, well-defined, rather broad, prominent, oblique, bent ridge; dorsal and ventral tips of ridge slightly widened, rounded, dorsal one pointing dorsalwards, ventral one pointing ventro-proximalwards and not merged with thickened ventral portion of LAP; inner side of distal edge with single large, poorly defined, oval, weakly prominent spur composed of more densely meshed stereom; inner side of tentacle notch rather small, deeply incised, sharply defined laterally. Very shallow, poorly defined vertical furrow dorsally bordering tentacle notch; no perforations discernible.

Remarks

The single specimen available differs markedly from co-occurring LAPs of Dermocoma subtilirugosa comb. nov. with respect to the much larger spine articulations on an elevated distal portion, the protruding spurs and the poorly developed vertical striation restricted to a narrow band near the spine articulations. Assignment to Dermocoma seems warranted on account of the position of the spine articulations in notches of the comparatively weakly elevated distal portion of the LAP, the ventro-proximalwards protruding ventral portion of the LAP and the shape of the ridge on the inner side. Within this genus, similarities are greatest with the LAPs of Dermocoma potti sp. nov. on account of the spine articulations which are not connected with the outer surface stereom, the rather poorly developed outer surface striation and the two poorly defined spurs on the outer proximal and inner distal edges. In view of the fact that many species of Dermocoma share almost indistinguishable LAP morphologies, this single record of an allegedly median LAP cannot be identified in more detail. It is likely that it represents a new species but in the absence of material it can at present only be listed as a new record of Dermocoma which differs markedly from co-occurring D. subtilirugosa comb. nov.

Figures

Fig. 25. Fossil skeletal plates and articulated arm fragments of ophiacanthid brittle stars; lateral arm plates (LAPs) in external (a) and internal (b) views. 1-3. Alternacantha dilionessa sp. nov. from the early Kimmeridgian of the Pointe du Chay, France. 1. GZG.INV.78666 (paratype), arm spine. 2. GZG. INV.78667 (paratype), median arm fragment in ventral view. 3. GZG.INV.78668 (paratype), proximal arm fragment in lateral (a) and dorsal (b) views. 4-5. Dermocoma subtilirugosa (Kristan-Tollmann & Gramann, 1992) comb. nov. from the Rhaetian (Late Triassic) of Fischerwiese, Austria. 4. GZG.INV.78671, proximal LAP. 5. GZG.INV.78672, median LAP. 6. Dermocoma sp. nov. innom. 1 from the Rhaetian (Late Triassic) of Fischerwiese, Austria; GZG.INV.78674, median LAP. One common scale bar per species except for 1.