Ophiomalleus stevenwilsoni, 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 : 184-185

Ophiomalleus stevenwilsoni sp. nov.

urn:lsid:zoobank.org:act:201BCFBC-5C34-4C2C-827A-30AF0F678279

Fig. 32 : 7-9

Diagnosis

Species of Ophiomalleus gen. nov. with large LAPs devoid of vertical striation on the outer surface and of spurs on the outer proximal and inner distal edges; up to four large, ear-shaped spine articulations not bordered proximally by a ridge; ridge on inner side of LAP very broad, with widened dorsal tip and shallow, poorly defined furrow in its centre.

Etymology

Species named in honour of British musician Steven Wilson, one of the contemporaneous masters of originality and creativity, whose music often taught me how to let ideas develop and materialise.

Type material

Holotype GZG.INV.78748 .

Paratypes

GZG.INV.78749 and GZG.INV.78750.

Type locality and horizon

Claypit Gott in Sarstedt, Germany; latest Hauterivian, Early Cretaceous.

Additional material

GZG.INV.78751 (7 dissociated LAPs).

Description

Holotype

GZG.INV.78748 is a dissociated, large, proximal LAP; slightly higher than wide; main portion of LAP nearly rectangular; dorsal and distal edges gently convex; proximal edge gently concave, devoid of spurs; ventral fifth of LAP large, strongly protruding ventro-proximalwards; outer surface with moderately finely meshed stereom, replaced by narrow and slightly sunken band of very finely meshed stereom along proximal edge. Four very large, ear-shaped spine articulations freestanding on elevated distal edge of LAP; spine articulations not bordered proximally by ridge; dorsal and ventral lobes merged into continuous volute; very strong dorsalward increase in size of spine articulations; gap between spine articulations and distal edge of LAP relatively narrow. Ventral edge of LAP with deeply incised but small tentacle notch.

Inner side of LAP with large, well-defined, prominent, broad ridge; ventral tip ventro-proximalwards bent, not merged with ventral portion of LAP; dorsal tip widened, round, dorso-proximalwards pointing; shallow, poorly defined furrow in the middle of the ridge, following its course; inner side of distal edge of LAP devoid of spurs; inner side of tentacle notch small, semi circular. Two minute perforations loosely arranged in vertical row dorsally bordering tentacle notch.

Paratype supplements and variation

GZG.INV.78749 is a dissociated median LAP; slightly wider than high; very well in agreement with holotype; ventral sixth of LAP strongly protruding ventro-proximalwards. Four spine articulations similar to those observed on holotype.

Inner side of LAP similar to that of holotype. Shallow, poorly defined, slightly oblique furrow dorsally bordering tentacle notch.

GZG.INV.78750 is a dissociated distal LAP; slightly wider than high; dorsal edge concave as a result of a constriction. Three spine articulations similar to those observed on holotype. Tentacle less deeply incised, small.

Ridge on inner side of LAP similar to that of holotype, slightly shorter and broader; furrow in the middle of the ridge slightly better defined. No perforations discernible.

Remarks

These LAPs are unequivocally assignable to Ophiomalleus gen. nov. on account of the massive, nearrectangular aspect of the main portion, the strongly protruding ventral portion, the shape and arrangement of the spine articulations and the shape of the ridge on the inner side. Within this genus, the LAPs described above are unique in entirely lacking vertical striation on the outer surface and spurs on the outer proximal and inner distal edges.

Figures

Fig. 32. Fossil skeletal plates of ophiacanthid brittle stars; lateral arm plates (LAPs) in external (a) and internal (b) views. 1. Ophiomitrella? sp. 2 from the Bathonian (Middle Jurassic) of Jumara, India; GZG. INV.78740, median to distal LAP. 2. Ophiomitrella sp. nov. from the late Maastrichtian (Late Cretaceous) of Maastricht, the Netherlands; NHMM JJ 5104, proximal LAP. 3-6. Ophiomalleus beneficarum gen. et sp. nov. from the Callovian of Bauer-Wehrland (3), Althüttendorf (4-5) and Hohensaaten (6), Germany. 3. GZG.INV.78741 (holotype), proximal to median LAP. 4. GZG.INV.78742 (paratype), proximal LAP. 5. GZG.INV.78743 (paratype), distal LAP. 6. GZG.INV.78744 (paratype), arm spine. 7-9. Ophiomalleus stevenwilsoni gen. et sp. nov. from the latest Hauterivian (Early Cretaceous) of Sarstedt, Germany. 7. GZG.INV.78748 (holotype), proximal LAP. 8. GZG.INV.78749 (paratype), median LAP. 9. GZG. INV.78750 (paratype), distal LAP. One common scale bar per species except for 6.