Ophiogaleus dorecki ( Hess, 1962 ) 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 : 110-112

Ophiogaleus dorecki ( Hess, 1962) comb. nov.

Fig. 20 : 1-2

p.p. Ophiacantha? dorecki Hess, 1962: 622 , figs 17, 19 (fig. 18 is a different species, probably not even an ophiacanthid).

non Ophiacantha? cf. dorecki – Kutscher 1996: 18, pl. 4, fig. 5 (probably an ophiomycetid close to extant Ophiohelus Lyman, 1880 ).

Diagnosis

Species of Ophiogaleus gen. nov. with relatively large LAPs displaying up to eleven spine articulations on the strongly elevated, yet proximally not sharply bordered, distal portion; no spurs discernible on outer proximal edge; up to three small, well-defined, strongly prominent spurs on inner distal edge of the LAP; ridge on the inner side with relatively narrow but vertically extremely elongate dorsal part.

Material examined

NHMB M1214, NHMB M 1215 and 35 dissociated LAPs from the late Pliensbachian of Seewen, Switzerland, the type material of Hess (1962).

Description

Large LAPs; proximal ones more than twice higher than wide; distal ones nearly as high as wide; dorsal edge slightly concave as a result of a moderately well-developed constriction; distal edge convex; proximal edge irregularly undulose, no spurs discernible; outer surface with moderately finely meshed stereom, replaced by more finely meshed stereom in very narrow band paralleling proximal edge of LAP. Eleven (proximal LAPs) to seven (distal LAPs) 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 not sharply bordered proximally; relatively narrow gap between spine articulations and distal edge of LAP; moderate (proximal LAPs) to weak (median and distal LAPs) dorsalward increase in size of spine articulations and of gaps separating them; row of spine articulations strongly (proximal LAPs) to weakly (distal ones) protruding ventralwards. Tentacle notch invisible in external view.

Inner side of LAPs with large, conspicuous, sharply defined, prominent ridge; short oblique central part of ridge; dorsal part widened, strongly vertically elongate, nearly triangular, with pointed (in proximal LAPs extremely elongate) dorsal tip, ventro-proximal tip slightly pointed; ventral portion of central part of ridge very short, ventro-proximally pointing, sharply separated from ventral part of LAP; inner side of distal edge of LAP with two to three small, well-defined, strongly prominent spurs composed of slightly more densely meshed stereom; inner side of tentacle notch relatively small, poorly defined laterally; moderately shallow, dorsally well-defined vertical furrow with small, irregular perforations dorsally bordering tentacle notch.

Remarks

Hess (1962) described the new species Ophiacantha ? dorecki on the basis of dissociated lateral arm plates from the Pliensbachian of Switzerland. A re-examination of the type material, however, has revealed that it actually includes two different LAP types, one similar to the holotype (see Hess 1962, fig. 17), the other resembling Hess’s (1962) fig. 18, characterised by a slightly oblique row of closely spaced spine articulations widely separated from the distal edge of the LAP. The higher-level taxonomic affinities of the latter type are unclear. Some features point to the Ophiacanthidae but the sigmoidal fold, one of the key diagnostic features of the family, could not be unambiguously observed in the specimens at hand.

In contrast, the LAP type, including the holotype, unquestionably belongs to the Ophiacanthidae . Within this family, strongest affinities are shared with the LAPs of Ophiogaleus constrictus comb. nov. and O. danicus comb. nov., on account of the number, shape and position of the spine articulations and the number of spurs on the inner distal edge of the LAP. The shape of the ridge on the inner side of the type specimens of Hess (1962) is admittedly rather unusual for Ophiogaleus gen. nov., but nevertheless compatible with the LAP morphological diagnosis of the genus. Within this genus, the LAPs are unique in displaying up to eleven spine articulations, lacking a ridge sharply bordering the spine articulations proximally and in having a relatively narrow but vertically extremely elongate dorsal part of the ridge on the inner side.

The LAPs described and illustrated by Kutscher (1996) as Ophiacantha ? cf. dorecki from the Toarcian/ Aalenian of Germany fundamentally differ from the type material of Hess (1962), in particular with respect to spine articulation morphology. The LAPs in question share greatest similarities with those of the extant ophiomycetid Ophiohelus .

Occurrence

Late Pliensbachian of Switzerland.

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.