Ophiogaleus stans, 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 : 112-114

Ophiogaleus stans sp. nov.

urn:lsid:zoobank.org:act:1B346B9F-A7E0-489B-B4DC-B87CCE351C95

Fig. 20 : 3-5

Diagnosis

Species of Ophiogaleus gen. nov. with relatively small LAPs; dorsalmost spine articulation enlarged; row of spine articulations slightly oblique; ventral part of the ridge on the inner side strongly bent.

Etymology

Name formed after stare, Latin for “staunch”, in reference to the very few type specimens of the species having been isolated, against all odds, from amongst more than 100 000 crinoid ossicles.

Type material

Holotype GZG.INV.78615 .

Paratypes

GZG.INV.78616 and GZG.INV.78617.

Type locality and horizon

La Pouza, France; Zigzag Zone, early Bathonian, Middle Jurassic.

Additional material

GZG.INV.78618 (3 dissociated LAPs).

Description

Holotype

GZG.INV.78615 is a dissociated, relatively small, proximal LAP; twice higher than wide; dorsal edge strongly concave as a result of a well-developed constriction; distal edge very weakly convex; proximal edge irregularly undulose, with large, moderately well-defined, prominent and strongly protruding, vertically elongate spur composed of more densely meshed stereom; outer surface with moderately coarsely meshed stereom, except for narrow band of finely meshed stereom paralleling proximal edge of LAP. Nine large, ear-shaped spine articulations freestanding in slightly oblique row on strongly elevated distal portion of LAP; dorsal and ventral lobes of spine articulations merged into continuous, round volute; spine articulations proximally sharply bordered by very weakly prominent, very narrow ridge becoming slightly undulose dorsalwards; large, dorsalwards increasing gap separating spine articulations and distal edge of LAP; spine articulations equi-distant and almost all of equal size; dorsalmost spine articulation much larger than remaining ones; row of spine articulations strongly protruding ventralwards. Ventral edge of LAP slightly convex; tentacle notch invisible in external view.

Inner side of LAP with large, conspicuous, sharply defined and strongly prominent ridge; ventral part of ridge narrow, strongly bent dorso-proximalwards; dorsal part of ridge very large, strongly widened, triangular, with pointed ventro-proximal angle and blunt dorsal tip; inner side of distal edge of LAP with medium-sized, moderately well-defined, round, weakly prominent spur composed of more densely meshed stereom; second smaller, less well-defined, almost indiscernible spur ventrally bordering large spur; inner side of tentacle notch very small. Shallow yet well-defined vertical furrow dorsally bordering centre of ventral ridge part; no perforations discernible in furrow.

Paratype supplements and variation

GZG.INV.78616 is a dissociated median LAP; ventro-proximal edge slightly fragmentary; slightly less than twice higher than wide; closely agreeing with holotype; distal edge convex; preserved portion of proximal edge slightly undulose, with very poorly defined, almost indiscernible, weakly prominent and non-protruding spur. Seven spine articulations similar to those observed on holotype, arranged in very slightly oblique row; gap separating spine articulations from distal edge narrower than in holotype, with very slight dorsalward increase in width; dorsalmost spine articulation much larger than remaining ones, as in holotype.

Inner side of LAP with ridge similar to that observed in holotype but with slightly narrower dorsal part; inner side of distal edge of LAP with three poorly defined, weakly prominent spurs, one medium-sized central one bordered dorsally and ventrally by smaller ones.

GZG.INV.78617 is a dissociated distal LAP; dorso-proximal corner slightly fragmentary; slightly higher than wide; distal edge convex. Seven spine articulations similar to those of holotype freestanding in vertical row on strongly elevated distal portion of LAP; ridge proximally sharply bordering spine articulations slightly wider and more strongly prominent than in holotype; gap between spine articulations and distal edge of LAP narrow; all spine articulations including the dorsalmost of equal size; row of spine articulations only slightly protruding ventralwards. Ventral edge of LAP with small concave tentacle notch.

Inner side of LAP with poorly defined ridge; ventral part short, bent, prominent; dorsal part widened, slightly fragmentary but originally nearly triangular, less prominent; no spurs on inner side of distal edge of LAP; inner side of tentacle notch moderately large. No furrow or perforations discernible.

Remarks

The highly distinctive shape of the ridge in combination with the number, position and arrangement of the spine articulations and the number of spurs on the inner distal edge unambiguously place these LAPs in Ophiogaleus gen. nov. The LAPs in question differ markedly from other types assigned to this genus on account of the enlarged dorsalmost spine articulation, the slightly oblique row of spine articulations in proximal LAPs, the strongly bent ventral part of the ridge on the inner side, and the lack of spurs in the distal LAP. Therefore, in spite of the limited amount of material available and its slightly fragmentary nature, this LAP type is here formally described as a new species.

Occurrence

Early Bathonian of France.

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.