Dermocoma potti, 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 : 143-145

Dermocoma potti sp. nov.

urn:lsid:zoobank.org:act:3AD371F8-AFD1-4629-A4FF-448A10F04AB1

Fig. 26 : 4-6

Diagnosis

Species of Dermocoma with large LAPs displaying a well-developed vertical striation; two moderately well-defined spurs on outer proximal and inner distal edge, dorsal one of which slightly larger and better defined; up to four relatively large spine articulations; ridge on inner side with strongly widened and dorsalwards pointing dorsal tip.

Etymology

Species named in honour of my friend and colleague Christian Pott, who will always find a moment to share and spread happiness.

Type material

Holotype GZG.INV.78675 .

Paratypes

GZG.INV.78676 and GZG.INV.78677.

Type locality and horizon

Feuguerolles, France; calcarenitic sediments infilling topography on surface of unconformity, late Pliensbachian, Early Jurassic.

Additional material

GZG.INV.78678 (63 dissociated LAPs).

Description

Holotype

GZG.INV.78675 is a dissociated, large, proximal to median LAP; slightly higher than wide; dorsal edge oblique, nearly straight; distal edge gently convex; ventral fifth of LAP protruding ventro-proximalwards; proximal edge of LAP gently concave, with large, moderately well-defined, prominent and pointedly protruding, horizontally elongate spur in the centre of the proximal edge; second smaller, less prominent and not protruding, weakly defined spur halfway between central spur and ventro-proximal tip of LAP; outer surface with very fine vertical striation composed of thin lamellae, very slightly overlapping distalwards, proximalwards slightly decreasing in size and fading into finely meshed stereom close to proximal edge of LAP. Four relatively large, ear-shaped spine articulations in tight notches of distal edge, interrupting vertical striation; spine articulations nearly equal-sized and equi-distant; dorsal and ventral lobes forming continuous volute; no connecting ridge between spine articulations and vertical striation; moderately wide gap between spine articulations and distal edge of LAP. Ventral edge of LAP with large, deeply concave tentacle notch.

Inner side of LAP with narrow, well-defined, prominent ridge, with very narrow, oblique central part, strongly widened dorsalwards pointing dorsal tip and short, narrow, ventro-proximalwards pointing ventral tip sharply separated from thickened ventral edge of LAP; inner side of distal edge of LAP with central, large, well-defined, horizontally elongate, prominent but not protruding spur composed of more densely meshed stereom; second, smaller and less well-defined spur close to ventro-distal edge of LAP. Inner side of tentacle notch distally bordered by short, oblique ridge. No perforations discernible on inner side of LAP.

Paratype supplements and variation

GZG.INV.78676 is a dissociated, median LAP; nearly as high as wide; dorsal edge straight; distal edge convex; ventral sixth of LAP slightly protruding; proximal edge of LAP weakly concave, with two very poorly defined, slightly prominent but not protruding spurs; vertical striation on outer surface limited to narrow band close to spine articulations, proximalwards fading into finely meshed stereom. Three spine articulations, ventralmost of which slightly smaller than remaining two; dorsal gap between spine articulations slightly larger than ventral one. Ventral edge of LAP with hardly discernible tentacle notch. Ridge on inner side of LAP well in agreement with that of holotype, ventral portion of ridge less well defined; two barely discernible spurs on inner side of distal edge. Inner side of tentacle notch large.

GZG.INV.78677 is dissociated, distal LAP; almost twice wider than high; of rectangular outline, with straight dorsal edge and slightly convex distal edge; proximal edge weakly concave, with two almost indiscernible, weakly prominent spurs; outer surface entirely covered by finely meshed stereom, no vertical striation. Two spine articulations in tight notches of distal edge; very narrow gap between spine articulations and distal edge of LAP. Ventral edge of LAP weakly convex, with small, weakly concave tentacle notch.

Inner side with short, oblique, well-defined ridge with pointed dorso-proximal and ventro-distal tips; two almost indiscernible, very weakly prominent spurs on inner side of distal edge of LAP. Tentacle notch narrow, deeply encompassed by thickened ventral edge.

Remarks

These LAPs are unambiguously assignable to Dermocoma on account of the size, shape and position of the spine articulations, the strongly protruding ventral portion of the LAPs and the shape of the ridge on the inner side. Within this genus, the presence of up to four spine articulations and two horizontally elongate spurs on the outer proximal edge makes it incompatible with any other currently known LAP type assigned to this genus. It is thus described here as a new species.

Occurrence

Late Pliensbachian 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.