Dermocoma longwyensis, 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 : 147-148

Dermocoma longwyensis sp. nov.

urn:lsid:zoobank.org:act:2EC1952C-3BD6-4708-9BD0-6FCB36214D97

Fig. 26 : 9-11

Diagnosis

Species of Dermocoma with relatively small LAPs displaying a well-developed, slightly undulose vertical striation; no discernible spurs on outer proximal edge in proximal LAPs; up to two, large, very poorly defined spurs on proximal edge in median to distal LAPs; single moderately well-defined spur on inner distal edge of proximal LAPs, two in median and distal LAPs; up to six large spine articulations; ventral lobe connected with distalwards projecting tip of outer surface stereom separating notches; ridge on inner side long, slender, devoid of thickened dorsal part.

Etymology

Named after Longwy, the type locality.

Type material

Holotype GZG.INV.78679 .

Paratypes

GZG.INV.78680 and GZG.INV.78681.

Type locality and horizon

Piedmont near Longwy, France; Laeviuscula Zone, early Bajocian, Middle Jurassic.

Additional material

GZG.INV.78682 (91 dissociated LAPs) from the early Bajocian of Longwy; GZG.INV.78683 (29 dissociated LAPs) from the Humphriesianum Zone, early Bajocian of Cirey-lès-Nolay, France.

Description

Holotype

GZG.INV.78679 is a dissociated, small, proximal LAP; slightly more than 1.5 times higher than wide; dorsal edge slightly convex; distal edge convex; proximal edge concave, devoid of well-developed, discernible spurs; ventral fifth of LAP strongy protruding ventro-proximalwards; outer surface with moderately fine, slightly undulose vertical striation composed of slightly overlapping, irregular lamellae and replaced by finely meshed stereom on proximal half of outer surface. Six large, ear-shaped spine articulations in notches of elevated distal portion of LAP; slighty dorsalward increase in size of spine articulations; gaps separating spine articulations clearly increasing in size larger towards dorsal edge of LAP; ventral and dorsal lobes of spine articulations merged into continuous volute; ventral lobe connected with distalwards projecting tips of outer surface stereom separating notches; spine articulations sharply bordered proximally by edge of notches rather than single distalmost lamella or ridge; notches incising vertical striation; narrow gap separating spine articulations and distal edge of LAP. Ventral edge of LAP with moderately large, concave tentacle notch.

Inner side of LAP with long, well-defined, prominent, rather slender ridge; ventral part of ridge gently bent, pointing ventro-proximalwards, merged ventrally with slightly thickened ventral portion of LAP; central part of ridge straight, oblique; dorsal part largely obscured by sediment, straight and almost vertical, not widened; three parts of ridge connected with very gentle, round kinks; inner side of distal edge of LAP with single small, moderately well-defined, very weakly prominent, round spur composed of densely meshed stereom; inner side of tentacle notch moderately large, well defined laterally; shallow, moderately well-defined vertical furrow with few small, scattered perforations dorsally bordering tentacle notch.

Paratype supplements and variation

GZG.INV.78680 is a dissociated median LAP; slightly less than 1.5 times higher than wide; very well in agreement with holotype; single large, slightly prominent, non-protruding, very poorly defined, almost indiscernible spur in ventral half of proximal edge. Five spine articulations similar to those observed on holotype.

Ridge on inner side of LAP better preserved; dorsal part straight, almost vertical, very close to proximal edge of LAP. Few small, scattered perforations loosely arranged in vertical row dorsally bordering tentacle notch.

GZG.INV.78681 is a dissociated distal LAP; slightly wider than high; proximal edge with two large, weakly prominent, non-protruding, very poorly defined, almost indiscernible spurs; vertical striation on outer surface more regular than in holotype. Four spine articulations similar to those observed on holotype; connection between ventral lobe of spine articulations and distalwards projecting tip of outer surface stereom separating notches very thin, weak. Ventral edge of LAP with small, weakly concave tentacle notch.

Ridge on inner side of LAP with oblique, slender dorsal part pointing dorso-proximalwards; ventral part of ridge widened, nearly triangular, separated from thickened ventral portion of LAP. Single, moderately large, irregular perforation dorsally bordering tentacle notch.

Remarks

These LAPs display all distinctive features to warrant assignment to the genus Dermocoma . The presence of up to six spine articulations is a feature shared with the LAPs of Dermocoma toarcensis comb. nov. and D. numbergerorum sp. nov. While the former differ in having up to three, rather than two, spurs on the outer proximal and inner distal edges, the latter display two much better-defined, widely separated spurs, a generally larger size and conspicuously large, wide ventral portions.

Occurrence

Early Bajocian of France.

Figures

Fig. 26. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-3. Dermocoma faberi sp. nov. from the Hettangian (Early Jurassic) of Vance, Belgium. 1. MnhnL HE408 (holotype), proximal LAP. 2. MnhnL HE409 (paratype), median LAP. 3. MnhnL HE410 (paratype), distal LAP. 4-6. Dermocoma potti sp. nov. from the late Pliensbachian (Early Jurassic) of Feuguerolles, France. 4. GZG.INV.78675 (holotype), proximal LAP. 5. GZG.INV.78676 (paratype), median LAP. 6. GZG. INV.78677 (paratype), distal LAP. 7-8. Dermocoma toarcensis (Hess, 1962) comb. nov. from the late Toarcian (Early Jurassic) of Seewen, Switzerland. 7. NHMB M11216, proximal LAP. 8. NHMB M11217, distal LAP. 9-11. Dermocoma longwyensis sp. nov. from the early Bajocian (Middle Jurassic) of Longwy, France. 9. GZG.INV.78679 (holotype), proximal LAP. 10. GZG.INV.78680 (paratype), median LAP. 11. GZG.INV.78681 (paratype), distal LAP. One common scale bar per species.