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 : 151

Dermocoma sp. 1

Fig. 27 : 3-4

Material examined

GZG.INV.78687 and GZG.INV.78688 from sample 95, lower Chari Formation, Callovian of Jumara, India; GZG.INV.78689 (dissociated LAP) from sample 24, Patcham Formation, late Bathonian of Jumara, India.

Description

GZG.INV.78687 is a dissociated, moderately large, proximal LAP; slightly higher than wide; dorsal edge fragmentary; distal edge convex; proximal edge irregularly concave, poorly preserved, no spurs discernible; ventral fifth of LAP strongly protruding ventro-proximalwards; outer surface with moderately coarse, regular vertical striation composed of very weakly overlapping lamellae replaced by finely meshed stereom on ventral portion of LAP and proximal third of outer surface. Four moderately large, equal-sized, ear-shaped spine articulations in shallow notches of slightly elevated distal edge of LAP; spine articulations proximally bordered by edge of notches; dorsal and ventral lobes of spine articulations merged into continuous volute; notches of spine articulations incising outer surface striation; very weak dorsalward increase in size of gaps separating spine articulations; probably very weak, thin connection between ventral lobe of spine articulations and distalwards projecting tip of outer surface stereom separating notches. Ventral edge of LAP with small, concave tentacle notch.

Inner side of LAP with relatively small, very slender, well-defined, slightly prominent ridge composed of ventro-proximalwards bent ventral part and nearly straight, oblique, dorso-proximalwards pointing, non-thickened dorsal part; no spurs discernible on inner side of distal edge of LAP; inner side of tentacle notch moderately small. No perforations or furrow discernible.

GZG.INV.78688 is a dissociated distal LAP; slightly less than 1.5 times wider than high; dorsal edge very weakly concave; proximal edge concave, with two small, poorly defined, prominent, weakly protruding, horizontally elongate spurs; vertical striation on almost entire outer surface. Three poorly preserved spine articulations similar to those observed in the specimen described above; weak dorsalward increase in size of spine articulations and of gaps separating them. Ventral edge of LAP gently convex; tentacle notch invisible in external view.

Inner side of LAP largely obscured by sediment; inner side of distal edge with two small, poorly defined, weakly prominent, horizontally elongate spurs; inner side of tentacle notch moderately small.

Remarks

In spite of its poor preservation, this material displays a distinctive combination of characters that warrants assignment to Dermocoma . The limited amount of material precludes a meaningful assessment at the species level. Nevertheless, it is worth recording this material since it is the first known record of Dermocoma from the Southern Hemisphere.

Occurrence

Late Bathonian to Callovian of India.

Figures

Fig. 27. Fossil lateral arm plates in external (a) and internal (b) views and articulated arm fragment of ophiacanthid brittle stars. 1-2. Dermocoma wrighti Hess, 1964 from the early Callovian (Middle Jurassic) of Liesberg, Switzerland. 1. NHMB M11218, proximal LAP. 2. NHMB M11219, distal LAP. 3-4. Dermocoma sp. 1 from the Callovian (Middle Jurassic) of Jumara, India. 3. GZG.INV.78687, proximal LAP. 4. GZG.INV.78688, distal LAP. 5-8. Dermocoma biformis (Hess, 1975) comb. nov. from the late Oxfordian (Late Jurassic) of Guldental, Switzerland (5-6) and Savigna, France (7-8). 5. NHMB M11220, proximal LAP. 6. NHMB M11221, distal LAP. 7. GZG.INV.78690, proximal LAP. 8. GZG. INV.78692, proximal arm fragment in ventral (a) and dorsal (b) views. One common scale bar for 1-2, 3-4, 5-6, 7 and 8 respectively.