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 : 158

Dermocoma sp. nov. innom. 2

Fig. 28 : 9

Material examined

GZG.INV.78705 from the Lacunosa Marls, early Kimmeridgian of Geisingen, Germany.

Description

GZG.INV.78705 is a small, dissociated median to distal LAP; slightly wider than high; dorsal edge weakly concave; distal edge convex, slightly oblique; proximal portion of LAP small, very weakly protruding ventro-proximalwards; proximal edge concave, with two very poorly defined, small, weakly prominent albeit protruding, horizontally elongate spurs; outer surface with poorly developed, irregular, vertical striation composed of slightly overlapping lamellae close to spine articulations, replaced by finely meshed stereom in proximal three-quarters of outer surface. Four large, ear-shaped spine articulations in shallow notches of very weakly elevated distal portion of LAP; strong dorsalward increase in size of spine articulations and of gaps separating them; dorsal and ventral lobes of spine articulations merged into continuous volute; row of spine articulations dorso-proximalwards receding; gap between spine articulations and distal edge of LAP narrow, widest near ventralmost spine articulation. Ventral edge of LAP nearly straight, with small, very shallow, almost indiscernible tentacle notch.

Inner side of LAP with relatively small, well-defined, prominent, oblique ridge with slender dorsoproximalwards pointing dorsal part and strongly widened, short, ventro-proximalwards pointing ventral part; inner side of distal edge of LAP with two moderately large, poorly defined, weakly prominent spurs; inner side of tentacle notch small, moderately well-defined laterally. No perforations or furrow discernible.

Remarks

In spite of the very limited amount of material available, this LAP type is clearly assignable to Dermocoma on account of the spine articulation structure, the two spurs on the outer proximal and inner distal edges, and the shape of the ridge on the inner side of the LAP. Both LAPs available are from median to even distal arm portions, which hampers a sound systematic assessment. It seems clear, however, that this LAP type is incompatible with any known species of Dermocoma on account of the oblique distal edge and similarly oblique row of spine articulations which display a strong dorsalward increase in size. In the absence of more material, in particular from proximal arm portions, the present LAP type is here treated as a new, still unnamed, species of Dermocoma .

Figures

Fig. 28. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-4. Dermocoma numbergerorum sp. nov. from the middle Oxfordian (Late Jurassic) of Foug, France. 1. GZG.INV.78695 (holotype), proximal LAP. 2. GZG.INV.78696 (paratype), proximal LAP. 3. GZG.INV.78697 (paratype), median LAP. 4. GZG.INV.78698 (paratype), distal LAP. 5-8. Dermocoma simonschneideri sp. nov. from the early Kimmeridgian (Late Jurassic) of the Pointe du Chay, France (5) and the late Kimmeridgian (Late Jurassic) of Trancoso, Portugal (6-8). 5. GZG.INV.78700 (holotype), proximal LAP. 6. GZG.INV.78701 (paratype), proximal LAP. 7. GZG.INV.78702 (paratype), median LAP. 8. GZG. INV.78703 (paratype), distal LAP. 9. Dermocoma sp. nov. innom. 2 from the early Kimmeridgian (Late Jurassic) of Geisingen, Germany; GZG.INV.78705, median to distal LAP.10-11. Dermocoma sp. nov.innom. 3 from the late Valanginian (Early Cretaceous) of the Ternberg Nappe, Austria. 10. NHMW 2012/0138/0009, proximal LAP. 11. NHMW 2012/0138/0010, distal LAP. One common scale bar per species.