Ophiochondrus punctatus ( Kutscher & Jagt, 2000 ) 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 : 209-211

Ophiochondrus punctatus ( Kutscher & Jagt, 2000) comb. nov. Fig. 37 : 4-5

Ophiacantha? punctata Kutscher & Jagt, 2000: 62-63 , pl. 25 figs 3-5.

Diagnosis

Species of Ophiochondrus with small LAPs displaying a coarsely meshed stereom on the outer surface with trabecular intersections strongly thickened into slightly vertically elongate granules or knobs; small, very poorly defined, weakly prominent and protruding spur on the outer proximal edge, paralleled on the inner distal edge by a moderately well-defined, rounded area of densely meshed stereom; up to eight small, slightly oval, spine articulations, proximally bordered by thick, slightly knobby ridge; gap between spine articulations and distal edge of LAP with trabecular intersections thickened into small granules; ridge on inner side relatively small, short.

Material examined

GZG.INV.78775, GZG.INV.78776 and 260 dissociated LAPs in the Manfred Kutscher Collection in Sassnitz, Germany, the type material of Kutscher & Jagt (2000).

Description

Small, dissociated LAPs, proximal ones slightly higher than wide, distal ones approximately 1.5 times wider than high; proximal to median LAPs of massive, thick, rounded aspect; dorsal edge straight (proximal LAPs) to concave (median and distal LAPs) as a result of a well-developed constriction; distal edge convex; proximal edge nearly straight, with small, very poorly defined, weakly prominent and very slightly protruding spur ventrally bordered by small, poorly defined, non-depressed area of slightly more finely meshed stereom; outer surface with coarsely meshed stereom slightly fining towards proximal edge; trabecular intersections of coarsely meshed stereom thickened into large, very weakly vertically elongate granules or knobs. Eight (proximal LAPs) to six (distal LAPs) small, ear-shaped, slightly oval spine articulations freestanding on weakly to fairly elevated distal portion of LAP; spine articulations proximally bordered by thick, well-defined, knobby ridge composed of vertically merged thickened trabeculae of coarsely meshed outer surface stereom; ventral and dorsal lobes of spine articulations separated proximally by very small notch; spine articulations nearly of equal size or with very weak dorsalward decrease in size; gap between spine articulations and distal edge of LAP at most as wide as one spine articulation, with dorsalward increase in width, with trabecular intersections of moderately finely meshed stereom thickened into small granules. Ventral edge of LAP weakly concave; tentacle notch invisible in external view.

Inner side of LAPs with relatively small, short, well-defined, prominent ridge with ventro-proximalwards bent ventral part not merged with ventral portion of LAP; dorsal tip of ridge slightly widened, with short ventro-proximalwards projecting extension; small, round knob distally bordering ridge in distal LAPs; inner side of distal edge of proximal to median LAPs with relatively small, moderately well-defined, round, very weakly protruding area of more densely meshed stereom; inner side of tentacle notch very small, shallow, moderately well defined laterally. No perforations or furrow discernible.

Remarks

Kutscher & Jagt (2000) described this LAP type from the early Maastrichtian of Germany and Denmark in detail and tentatively assigned it to Ophiacantha using open nomenclature. They stressed, however, that this assignment was highly doubtful when the fossil LAPs were compared with those of extant species of Ophiacantha . Thanks to a systematic SEM-supported assessment of LAP morphologies in Recent ophiacanthids performed in the course of the present study, it is now possible to constrain the generic placement of these LAPs even further. Strongest similarities are shared with the LAPs of Ophiochondrus , mainly on account of the massive, thick, rounded general aspect of the LAPs, the shape, size and position of the spine articulations, the outer surface ornament, and the shape of the ridge on the inner side. It is the first fossil record of Ophiochondrus or at least of a very closely related, extinct genus.

The LAPs of Ophiochondrus punctatus comb. nov. cannot be confused with any other fossil type of LAP. Those of co-occurring Ophiochondrus ? semirotundus ( Kutscher & Jagt, 2000) comb. nov. have fewer spine articulations not bordered proximally by a ridge, and large contact surfaces with the opposite LAP on the inner side. LAPs assigned to Inexpectacantha display strongly tilted spine articulations with a ventral lobe commonly merged with the outer surface stereom, and a ridge on the inner side lacking the ventro-proximalwards projecting extension.

Occurrence

Early Maastrichtian of Germany and Denmark.

Figures

Fig. 37. Lateral arm plates (LAPs) of fossil and Recent ophiacanthid brittle stars in external (a) and internal (b) views. 1-2. Ophiochondrus convolutus Lyman, 1869, Recent. 1. Proximal LAP. 2. Median LAP. 3. Ophiochondrus stelliger Lyman, 1879, Recent; proximal LAP. 4-5. Ophiochondrus punctatus (Kutscher & Jagt, 2000) comb. nov. from the early Maastrichtian (Early Cretaceous) of Rügen, Germany. 4. GZG.INV.78775, proximal LAP. 5. GZG.INV.78776, distal LAP. 6-7. Ophiochondrus? semirotundus (Kutscher & Jagt, 2000) comb. nov. from the early Maastrichtian of Rügen, Germany. 6. GZG.INV.78800, proximal LAP. 7. GZG.INV.78801, median LAP. 8-9. Ophiacanthidae gen. et sp. nov. innom. from the late Oxfordian (Late Jurassic) of the Plettenberg, Germany. 8. GZG.INV.78802, proximal LAP. 9. GZG.INV.78803, median or distal LAP. 10-11. Ophiojagtus argoviensis (Hess, 1966) comb. nov. from the late Oxfordian (Late Jurassic) of Savigna, France. 10. NHMB M1124, proximal LAP. 11. NHMB M11225, proximal to median LAP. One common scale bar per species.