Dermocoma simonschneideri, 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 : 156-158

Dermocoma simonschneideri sp. nov.

urn:lsid:zoobank.org:act:D3449C2A-A9F1-42F1-87B0-CB8E0210232A

Fig. 28 : 5-8

Diagnosis

Species of Dermocoma with large LAPs displaying a very well-developed vertical striation on at least half of the outer surface; large, oval and conspicuously oblique spur on proximal edge; four spine articulations sunken in deep notches of a poorly elevated distal LAP portion; ridge on inner side very slender, with ventral tip merged with ventral portion of LAP, and dorsal tip slightly widened and merged with proximal edge of LAP.

Etymology

Species named in honour of Simon Schneider, who kindly provided the samples yielding the type material of the species.

Type material

Holotype GZG.INV.78700 .

Paratypes

GZG.INV.78701, GZG.INV.78702 and GZG.INV.78703 from the late Kimmeridgian (Late Jurassic) of Trancoso, Portugal.

Type locality and horizon

Pointe du Chay near La Rochelle, France; Achilles Subzone, Cymodoce Zone , early Kimmeridgian, Late Jurassic.

Additional material

GZG.INV.78704 (14 dissociated LAPs) from the Amaral Formation, late Kimmeridgian of Trancoso, Portugal.

Description

Holotype

GZG.INV.78700 is a dissociated, large, proximal to median LAP; slightly higher than wide; dorsal and distal edges convex; proximal edge irregularly concave, with large, moderately well-defined, slightly prominent, non-protruding, oval and conspicuously oblique spur; ventral quarter of LAP strongly protruding ventro-proximalwards; distal half of outer surface with very well-developed, fine, regular vertical striation composed of overlapping lamellae, replaced by finely meshed stereom on proximal half of outer surface. Four relatively large, ear-shaped, nearly equal-sized spine articulations in deep notches of slightly elevated distal portion of LAP; ventral lobe merged with dorsal one into continuous volute but only weakly connected with distally projecting tip of outer surface between notches; spine articulations proximally sharply separated by edge of notches; weak dorsalward increase in size of gaps separating spine articulations; gap between spine articulations and distal edge of LAP very narrow. Ventral edge of LAP with small, weakly concave tentacle notch.

Inner side of LAP with moderately large, very slender, gently bent ridge; ventral tip pointing ventralwards, merged with ventral portion of LAP; dorsal tip pointing dorso-proximally, slightly widened and merged with proximal edge of LAP; inner side of distal edge of LAP with small, well-defined, prominent, oval and oblique spur composed of densely meshed stereom; inner side of tentacle notch relatively large, with coarsely meshed, horizontally elongate stereom; well defined laterally. Short, shallow, rather broad, irregular and slightly oblique furrow with highly variable perforations dorsally bordering tentacle notch.

Paratypes

GZG.INV.78701 is a dissociated proximal LAP; approximately 1.5 times higher than wide; very well in agreement with holotype; outer surface less well defined, vertical striation not discernible. Four spine articulations similar to those of holotype.

Inner side of LAP with ridge similar to that of holotype but slightly longer; spur on inner side of distal edge poorly defined. Short, slightly oblique furrow as in holotype but distally bordered by broad, poorly defined and weakly prominent ridge.

GZG.INV.78702 is a dissociated median LAP; slightly wider than high; very well in agreement with holotype; vertical striation slightly finer and on distal two-thirds rather distal half of outer surface. Four spine articulations slightly smaller than those observed on holotype, otherwise similar.

Ridge on inner side of LAP with more strongly widened dorsal tip; spur on inner side of distal LAP edge very poorly defined, almost indiscernible. No perforations or furrow discernible.

GZG.INV.78703 is a dissociated distal LAP; more than 1.5 times wider than high; dorsal edge slightly concave as a result of a very weak constriction; proximal edge with two moderately well-defined spurs, dorsal one of which largest; vertical striation on three-quarters of outer surface. Four spine articulations smaller than those of holotype and poorly preserved, otherwise similar. Tentacle notch invisible in external view.

Inner side of LAP with small, sharply defined ridge, with pointed, proximalwards bent dorsal tip, and widened ventral tip, not merged with ventral portion of LAP; inner side of distal edge of LAP with two poorly defined, large, oval, weakly prominent spurs; inner side of tentacle notch small, oblique, laterally well defined. Single, relatively large perforation dorsally bordering tentacle notch.

Remarks

In spite of the limited amount of material available, these LAPs are unambiguously assignable to the genus Dermocoma on account of the highly characteristic combination of the strongly protruding ventral portion of the LAP, the nearly equal-sized spine articulations in regularly spaced notches of the weakly elevated distal portion of the LAP, and the simple ridge on the inner side devoid of sharp kinks or conspicuously widened parts. The single large, conspicuously oblique spur on the outer proximal and inner distal edges of the proximal and median LAPs is a highly distinctive feature not found in any other species assigned to Dermocoma .

Occurrence

Early Kimmeridgian of France and late Kimmeridgian of Portugal.

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.