Ophiogaleus, 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 : 114-115

Ophiogaleus sp. nov. innom. 2

Fig. 20 : 6-7

Material examined

GZG.INV.78619, GZG.INV.78620, GZG.INV.78621 (20 dissociated LAPs) from sample 95, lower Chari Formation, Callovian of Jumara, India; GZG.INV.78622 (dissociated LAP) from sample 31, lower Chari Formation, Callovian, Jumara, India; GZG.INV.78623 (dissociated LAP) from sample 121, upper Chari Formation, Callovian of Jumara, India.

Description

GZG.INV.78619 is a dissociated, moderately large, proximal LAP; ventral edge fragmentary, originally probably 1.5 times higher than wide; dorsal edge nearly straight; distal edge convex; proximal edge irregularly undulose with three moderately large, poorly defined, round to vertically slightly elongate, prominent and weakly protruding spurs, two closely spaced ones in the middle of the proximal edge, and one in the dorsal half of the proximal edge; outer surface with moderately coarsely meshed stereom; trabeculae of outer surface stereom merging into very weakly developed vertical striation close to ventral edge of LAP. At least five large, ear-shaped spine articulations; ventral and dorsal lobes merged into continuous volute; very weak dorsalward increase in size of spine articulations and slightly stronger increase in size of gaps separating them; spine articulations proximally sharply bordered by slightly undulose, well-defined, prominent, relatively broad ridge; gap between spine articulations and distal edge of LAP narrow.

Inner side of LAP with relatively small, well-defined, prominent, oblique ridge with widened, triangular ventral part and widened, vertically elongate, triangular dorsal part with dorsalwards and ventroproximally pointing angles; inner side of distal edge of LAP with at least two relatively large, poorly defined, round, weakly prominent spurs composed of more densely meshed stereom; inner side of tentacle notch relatively small, deeply incised, partly obscured by sediment; laterally well defined. No perforations or furrow discernible.

GZG.INV.78620 is a dissociated distal LAP; slightly wider than high; well in agreement with abovedescribed LAP; dorsal edge weakly concave as a result of a constriction; single, large, poorly defined, round, prominent and weakly protruding spur on proximal edge. Five spine articulations similar to those observed in other specimen. Ventral edge slightly convex, with very small, gently concave tentacle notch.

Inner side of LAP with relatively small, inconspicuous oblique ridge displaying strongly widened, triangular ventral part and slightly widened dorsal tip; single large, moderately well-defined, round, very weakly prominent spur composed of densely meshed stereom on inner side of distal edge of LAP.

Remarks

In spite of the rather poor preservation, these specimens are assignable to Ophiogaleus gen. nov. on account of the highly distinctive shape of the ridge on the inner side, the shape and position of the spine articulations and the presence of more than one spur on the outer proximal and inner distal edges, at least in proximal LAPs. Admittedly, the number of spine articulations is atypically low for Ophiogaleus gen. nov., although it appears likely that this is an artefact of the fragmentary condition of the proximal LAPs. There is a certain resemblance with the LAPs assigned herein to Ophiomitrella , especially on account of the conspicuous ridge proximally bordering the spine articulations. However, the shape of the ridge on the inner side of the LAPs differs fundamentally.

The low number of spine articulations and the poorly developed vertical striation near the ventral edge of the outer surface suggest that the above-described LAPs belong to a new species. In the absence of more complete and better-preserved material, however, the LAPs in question cannot be formally described.

Figures

Fig. 20. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views and articulated arm fragment. 1-2. Ophiogaleus dorecki (Hess, 1962) comb. nov. from the late Pliensbachian (Early Jurassic) of Seewen, Switzerland. 1. NHMB M11214, proximal LAP. 2. NHMB M11215, distal LAP. 3-5. Ophiogaleus stans sp. nov. from the early Bathonian (Middle Jurassic) of La Pouza, France. 3. GZG.INV.78615 (holotype), proximal LAP. 4. GZG.INV.78616 (paratype), median LAP. 5. GZG.INV.78617 (paratype), distal LAP. 6-7. Ophiogaleus sp. nov. innom 2 from the Callovian (Middle Jurassic) of Jumara, India. 6. GZG.INV.78619, proximal LAP. 7. GZG.INV.78620, distal LAP. 8-10. Ophiogaleus constrictus (Hess, 1966) comb. nov. from the late Oxfordian (Late Jurassic) of Savigna, France.8. GZG.INV.78624, proximal LAP. 9. GZG.INV.78625, distal LAP. 10. GZG.INV.78626, proximal arm fragment in ventral (a) and dorsal (b) views. One common scale bar per species except for 10.