Ophiogaleus danicus ( Rasmussen, 1952 ) 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 : 119-120

Ophiogaleus danicus ( Rasmussen, 1952) comb. nov.

Fig. 21 : 3-4

Ophiacantha ? danica Rasmussen, 1952: 52, fig. 6.

Ophiacantha? danica – Jagt 1999a: 199 , pl. 1 fig. 8. — Kutscher & Jagt 2000: 61, pl. 24 figs 7-9, pl. 25 figs 1-2 [non pl. 24 fig. 10, which most probably is an LAP of Ophiotreta striata (see above)]. — Jagt & Odin 2001: 416, pl. 1 fig. 1.

p.p. Ophiacantha? danica – Jagt 2000: 10, pl. 2 fig. 10 [non pl. 2 figs 5-7, Ophiomitrella sp. nov. (see below)]

Diagnosis

Species of Ophiogaleus gen. nov. with very large LAPs displaying coarsely meshed stereom on the outer surface with strongly thickened trabecular intersections, especially in ventral part of the LAPs developed into large granules; up to four variably developed spurs on outer proximal and inner distal edges of proximal to distal LAPs; up to eleven spine articulations sharply separated proximally by thick, well-defined, prominent ridge.

Material examined

GZG.INV.78635, GZG.INV.78636, and 328 dissociated LAPs from the early Maastrichtian of Rügen, the original material of Kutscher & Jagt (2000); 16 dissociated LAPs from the early Maastrichtian of Lägerdorf-Kronsmoor, Germany.

Description

Very large LAPs; more than twice wider than high (proximal LAPs) to slightly wider than high (distal ones); dorsal edge strongly concave as a result of a well-developed constriction; distal edge convex; proximal edge irregularly convex, with one to four moderately well-defined, prominent, rarely protruding, oval spurs of variable size and position in proximal to distal LAPs; outer surface with coarsely meshed stereom, trabecular intersections strongly thickened, in ventral part of LAP developed into large, conspicuous granules; more finely meshed stereom in narrow band paralleling proximal edge of LAP. Eleven (proximal LAPs) to five (distal ones) large, ear-shaped spine articulations freestanding on strongly elevated distal portion of LAP; dorsal and ventral lobes of spine articulations merged into continuous volute; spine articulations proximally sharply bordered by thick, well-defined, prominent, slightly knobby and wavy ridge; gap between spine articulations and distal edge of LAP slightly narrower than one spine articulation; very weak dorsalward increase in size of spine articulations and of gaps separating them; row of spine articulations slightly protruding in proximal to median LAPs. Ventral edge of LAP slightly concave; tentacle notch not visible in external view.

Inner side of LAPs with large, broad, conspicuous, sharply defined and prominent ridge; ventral part of ridge relatively short, moderately wide, strongly bent; dorsal part of ridge conspicuously large, triangular, vertically elongate, dorsal and ventro-proximal tips pointed, proximal and ventral edges slightly concave, distal edge slightly convex; inner side of distal edge of LAP with one to four variably well-defined, slightly prominent, non-protruding, oval spurs of variable size and position; inner side of tentacle notch very small, slightly oblique, poorly defined. Well- to moderately well-defined, narrow, vertical furrow with very small perforations dorsally bordering tentacle notch in proximal and median LAPs.

Remarks

Ophiogaleus danicus comb. nov. was originally described by Rasmussen (1952) from the late Maastrichtian of Denmark. The brief description and single illustration was beautifully complemented by Kutscher & Jagt (2000) on the basis of new material from the Maastrichtian of Germany and Denmark. Those authors retained the species in the genus Ophiacantha , albeit in open nomenclature, although they speculated about close similarities with the LAPs of extant Ophiomitra Lyman, 1869 . In that genus, however, the shape of the ridge on the inner side differs fundamentally. In contrast, striking similarities are shared with the LAPs of Ophiogaleus constrictus comb. nov. from the Oxfordian of France and Switzerland (see above), in particular with regard to the shape of the ridge, the number, shape and position of the spine articulations, and the outer surface ornament. Thus, the present species is here transferred to Ophiogaleus gen. nov., which is in line with Rasmussen’s (1952) initial tentative assignment to Ophiacantha considering that both genera share highly similar LAP morphologies and thus most probably are also phylogenetically close.

One of the specimens illustrated by Kutscher & Jagt (2000, pl. 24, fig. 10) does not belong to Ophiogaleus danicus comb. nov. but most probably to Ophiotreta striata comb. nov. (see above). The specimens illustrated by Jagt (2000, pl. 2, figs 5-7) almost all belong to a yet undescribed species of Ophiomitrella (see below).

Occurrence

Late Campanian of Belgium and France, Maastrichtian of Germany and Denmark.

Figures

Fig. 21. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views and articulated arm fragment in ventral (a) and dorsal (b) views. 1. Ophiogaleus constrictus (Hess, 1966) comb. nov. from the late Oxfordian (Late Jurassic) of Savigna, France; GZG.INV.78627 distal arm fragment. 2. Ophiogaleus sp. from the early Kimmeridgian (Late Jurassic) of Geisingen, Germany; GZG.INV.78632, proximal LAP. 3-4. Ophiogaleus danicus (Rasmussen, 1952) comb. nov. from the early Maastrichtian (Late Cretaceous) of Rügen, Germany. 3. GZG.INV.78635, proximal LAP. 4. GZG. INV.78636, distal LAP. 5-6. Hanshessia sp. nov. innom. 1 from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 5. NHMW 2012/0137/0021, proximal LAP. 6. NHMW 2012/0137/0022, proximal LAP. 7-9. Hanshessia sp. nov. innom. 2 from the early Bathonian (Middle Jurassic) of La Pouza, France. 7. GZG.INV.78637, proximal LAP. 8. GZG.INV.78638, proximal LAP. 9. GZG.INV.78639, distal to median LAP. One common scale bar per species except for 1.