Dermacantha seeweni ( Kutscher & Hary, 1991 ) Thuy, 2013

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 : 164-165

Dermacantha seeweni ( Kutscher & Hary, 1991) comb. nov. Fig. 29 : 6-8

Ophiocten? seeweni Kutscher & Hary, 1991: 46 , pl. 1 fig. 3a-d.

non Ophiocten? seeweni – Kutscher 1996: 15, pl. 2 figs 1-5. — Kutscher & Villier 2003: 189, pl. 5 figs 8-9, pl. 6 figs 1-2.

Diagnosis

Species of Dermacantha gen. nov. with small LAPs displaying a well-developed, very fine vertical striation on distal half of outer surface, composed of merged trabeculae of finely meshed stereom; single, very poorly defined spur on outer proximal and inner distal edges of proximal LAPs; up to five small spine articulations in notches of non-elevated distal portion of LAP; ventral and dorsal lobes of spine articulations separated by two to three small knobs; ventral lobe larger than dorsal one, projecting ventro-proximalwards.

Type locality and horizon

Bishop’s Cleeve near Cheltenham, Great Britain; lowest part of the claypit, Obtusum Zone, late Sinemurian, Early Jurassic.

Material examined

GZG.INV.78706, GZG.INV.78707, GZG.INV.78708 and GZG.INV.78709 (9 dissociated LAPs) from the late Sinemurian of Bishop’s Cleeve, Great Britain; the type material of Kutscher & Hary (1991).

Description

Small, LAPs; proximal ones slightly higher than wide, distal ones slightly wider than high; dorsal edge slightly convex; distal edge convex; proximal edge irregularly undulose, with single poorly defined, almost indiscernible, weakly prominent, horizontally elongate, non-protruding spur near ventral edge in proximal to median LAPs, two very poorly defined, almost indiscernible, horizontally elongate, weakly prominent spurs in distal LAPs; ventral fifth of LAP protruding ventro-proximalwards; ventro-distal tip of LAP protruding ventralwards, rounded; outer surface with finely meshed stereom, trabeculae of which merged into fine, irregular vertical striation in distal half of outer surface; very narrow band of finely, faintly horizontally striped stereom along proximal edge of LAP. Five (proximal LAPs) to four (median to distal LAPs) moderately large, ear-shaped spine articulations in notches of non-elevated distal portion of LAP; ventral and dorsal lobes of spine articulations separated by two to three small knobs; ventral lobe larger than dorsal one, ventro-distalwards projecting; spine articulations not sharply bordered proximally, directly encompassed by finely meshed outer surface stereom; gap between spine articulations and distal edge of LAP moderately large, approximately as wide as half the width of a spine articulation; very weak dorsalward increase in size of spine articulations; dorsalmost gap between spine articulations slightly larger than remaining ones. Ventral edge of LAP with moderately large, concave tentacle notch.

Inner side of LAP with large, sharply defined, prominent, long, oblique, nearly straight, relatively narrow ridge; dorsal tip of ridge slightly widened, pointing dorso-proximalwards; ventral part of ridge bent, pointing ventro-proximalwards, separated from thickened ventral edge; inner side of distal edge of LAP with very weakly defined, almost indiscernible spur; inner side of tentacle notch relatively large, well defined laterally, with coarsely meshed, very slightly horizontally elongate stereom. No perforations or furrow discernible.

Remarks

The relatively small spine articulations with the discontinuous volute combined with a general Dermocoma -like morphology unquestionably place these LAPs in Dermacantha gen. nov. Within this, these LAPs are unique in displaying conspicuously distally projecting ventral lobes of the spine articulations, and are thus described here as a new species.

Occurrence

Early Sinemurian of Luxembourg and late Sinemurian of Great Britain.

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.