Eolaxoporus, 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 : 22

Eolaxoporus sp.

Fig. 6 : 1

Material examined

MHI 2083/1 (dissociated LAP) from the uppermost Anisian (middle Triassic) Trochitenkalk of Oberscheffach, Germany.

Description

MHI 2083/1 is a dissociated, very small, median LAP of near-rectangular outline; approximately 1.5 times wider than high; dorsal edge concave as a result of a well-developed constriction; distal edge slightly convex; ventro-distal tip of LAP slightly protruding; proximal edge concave, too poorly preserved for spurs to be discernible; no conspicuous ornamentation seen on outer surface; mesh size of stereom on outer surface unknown. Four large, ear-shaped spine articulations on slightly elevated distal part of LAP; dorsal and ventral lobes of spine articulations proximally widely separated, horizontally elongate, nearly parallel and slightly arched concentrically; slight dorsalward increase in the size of the spine articulations. Ventral edge of LAP with large, slightly concave tentacle notch.

Inner side of LAP with large, well-defined, bent ridge; dorsal tip of ridge rounded, not widened, pointing dorso-proximalwards; ventral tip of ridge separated from ventral edge of LAP; inner side of distal edge of LAP with two large, poorly defined, slightly prominent spurs, one near the dorso-distal tip and the second near the ventro-distal tip of the LAP.

Remarks

The single LAP described above is poorly preserved. Yet, it is an important specimen since it is unambiguously assignable to Eolaxoporus gen. nov. on account of the general shape of the LAP, the constriction, the highly distinctive shape of the spine articulations and of the ridge on the inner side, and the very large tentacle notch, and thus documents the presence of the genus in strata as old as Anisian. The specimen shows closest similarities to E. hagdorni sp. nov. but its poor preservation precludes any more detailed comparison on the species level.

Figures

Fig. 6. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1. Eolaxoporus sp. from the latest Anisian (Middle Triassic) of Oberscheffach, Germany, MHI 2083/1, median LAP. 2-4. Eolaxoporus hagdorni gen. et sp. nov. from the late Carnian (Late Triassic) of Jushui, China. 2. MHI 2084/1 (holotype), proximal LAP. 3. MHI 2085/1 (paratype), median LAP. 4. MHI 2086/1 (paratype), distal LAP. 5. Eolaxoporus sp. nov. innom. from the early Carnian (Late Triassic) of Milieres, Italy; GZG.INV.78500, proximal to median LAP. 6-8. Eolaxoporus imminens gen. et sp. nov. from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 6. NHMW 2012/0137/0001 (holotype), proximal LAP. 7. NHMW 2012/0137/0002 (paratype), median LAP. 8. NHMW 2012/0137/0003 (paratype), distal LAP. One common scale bar per species is given.