Ophiacantha reginae, 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 : 105-106

Ophiacantha reginae sp. nov.

urn:lsid:zoobank.org:act:283B7CEB-644F-4997-A2FE-EFAED468A3BD

Fig. 19 : 3-5

Diagnosis

Species of Ophiacantha with moderately large LAPs; outer surface stereom rather finely meshed, devoid of vertical striation; no spur on outer proximal and inner distal edges; up to seven spine articulations on strongly elevated distal portion of LAP; row of spine articulations strongly protruding dorsalwards.

Etymology

Species named in honour of Regina Fischer , who generously provided the sample yielding the type material of the species.

Type material

Holotype GZG.INV.78605 .

Paratypes

GZG.INV.78606 and GZG.INV.78607.

Type locality and horizon

Alsen quarry, Lägerdorf, Germany; Galerites vulgaris Zone, late Campanian, Late Cretaceous.

Additional material

GZG.INV.78608 (one dissociated LAP).

Description

Holotype

GZG.INV.78605 is a dissociated, moderately large, proximal LAP; slightly higher than wide; dorsal edge strongly concave as a result of a well-developed constriction; distal edge weakly convex; proximal edge concave, devoid of spurs; outer surface with moderately finely meshed stereom. Seven large, earshaped, round spine articulations on strongly elevated distal portion of LAP; very weak dorsalward increase in size of spine articulations and of gaps separating them; dorsal and ventral lobes of spine articulations merged into continuous, round volute; spine articulations proximally bordered by sharply defined, straight edge of strongly elevated distal portion of LAP; gap between spine articulations and distal edge of LAP from slightly narrower to clearly wider than one spine articulation, with dorsalward increase in width; row of spine articulations conspicuously protruding dorsalwards. Ventral edge of LAP convex, slightly pointed; tentacle notch invisible in external view.

Inner side of LAP with large, well-defined, prominent ridge; main part of ridge straight, oblique, dorsal tip widened and merged with rather short ventrally projecting extension; ventral part of ridge slightly shorter than main part, gently bent, ventro-proximally bent, not merged with ventral portion of LAP; kink between ventral and main part of ridge rounded, slightly thickened; inner side of distal edge of LAP devoid of spurs; inner side of tentacle notch small, poorly defined, shallow. No perforations or furrow discernible.

Paratype supplements and variation

GZG.INV.78606 is a dissociated median LAP; nearly as high as wide; dorso-proximal tip slightly fragmentary; very well in agreement with holotype. Six spine articulations similar to those observed on holotype; edge of strongly elevated distal portion of LAP proximally bordering spine articulations slightly undulose. Ventral edge of LAP nearly straight.

Ridge on inner side of LAP similar to that of holotype but with slightly bent main part; very shallow, poorly defined vertical furrow dorsally bordering tentacle notch, with single, small perforation at dorsal end of furrow.

GZG.INV.78607 is a dissociated distal LAP; nearly 1.5 times wider than high; ventro-proximal tip of LAP fragmentary. Five spine articulations similar to those of holotype; edge of strongly elevated distal portion of LAP proximally bordering spine articulations slightly undulose; row of spine articulations less strongly protruding dorsalwards than in holotype.

Ridge on inner side of LAP similar to that of holotype but with smaller, less well-defined ventralward projecting extension of dorsal tip. Irregular perforations loosely arranged in vertical row dorsally bordering tentacle notch.

Remarks

The structure and position of the spine articulations, the shape of the ridge and the absence of spurs on the outer proximal and inner distal edges strongly suggest that these LAPs are assignable to Ophiacantha . The conspicuously dorsally protruding row of spine articulations clearly differentiates this LAP type from other types assigned to that genus. While, at first sight, this character might seem unusual for Ophiacantha , it is not uncommon among Recent species of the genus such as O. duplex Koehler, 1897 and O. serrata Lyman, 1878 , which otherwise perfectly match the LAP morphology of Ophiacantha in its proper sense.

Occurrence

Late Campanian of Germany.

Figures

Fig. 19. Fossil skeletal plates of ophiacanthid brittle stars; lateral arm plates (LAPs) in external (a) and internal (b) views. 1-2. Ophiacantha sp. nov. innom 3 from the middle Albian (Early Cretaceous) of Folkestone, Great Britain. 1. GZG.INV.78602, proximal LAP. 2. GZG.INV.78603, distal LAP. 3-5. Ophiacantha reginae sp. nov. from the late Campanian (Late Cretaceous) of Lägerdorf-Alsen, Germany. 3. GZG.INV.78605 (holotype), proximal LAP. 4. GZG.INV.78606 (paratype), median LAP. 5. GZG.INV.78607 (paratype), distal LAP. 6-9. Ophiacantha steffenschneideri sp. nov. from the Rupelian (Oligocene) of Bad Freienwalde, Germany. 6. GZG.INV.78609 (holotype), proximal LAP. 7. GZG.INV.78610 (paratype), median LAP. 8. GZG.INV.78611 (paratype), distal LAP. 9. GZG. INV.78612 (paratype), arm spine. 10-12. Ophiogaleus sp. nov. innom 1 from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 10. NHMW 2012/0137/0017, proximal LAP. 11. NHMW 2012/0137/0018, proximal to median LAP. 12. NHMW 2012/0137/0019, proximal to median LAP. One common scale bar per species except for 9.