Eolaxoporus imminens, 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 : 25-27

Eolaxoporus imminens sp. nov.

urn:lsid:zoobank.org:act:698BEA08-2562-4B83-9062-C09DC982E9A3 Fig. 6 : 6-8

Diagnosis

Species of Eolaxoporus gen. nov. with moderately small LAPs displaying a relatively high height/width ratio; very poorly defined spurs on outer proximal edge; up to five, strongly oblique spine articulations; ridge on inner side of LAP relatively long and slender.

Etymology

Species name formed after imminere, Latin for “reaching” or “hanging over”, in reference of the species being the only known Jurassic species of the otherwise exclusively Triassic Eolaxoporus gen. nov.

Type material

Holotype

NHMW 2012/0137/0001 .

Paratypes

NHMW 2012/0137/0002 and NHMW 2012/0137/0003.

Type locality and horizon

Glasenbach Gorge, Austria; Hauptknollenbrekzie, late Sinemurian to early Pliensbachian, Early Jurassic.

Additional material

NHMW 2012/0137/0004 (6 dissociated LAPs).

Description

Holotype

NHMW 2012/0137/0001 is a dissociated, small, proximal LAP; slightly higher than wide; ventro-distal tip of LAP not protruding; dorsal edge strongly concave as a result of a well-developed constriction; distal edge gently convex; proximal edge strongly concave, with two small, very poorly defined, slightly prominent spurs, one in the middle of the proximal edge, protruding, the second one near the ventroproximal tip of the LAP, not protruding; outer surface without conspicuous ornamentation; finely meshed stereom, becoming slightly more finely meshed towards proximal edge and towards spine articulations. Five large, ear-shaped spine articulations on elevated distal part of LAP; dorsalward increase in size of spine articulations and, a little less strongly, in gaps separating them; spine articulations composed of near-parallel, concentrically arched dorsal and ventral lobes, tilted and therefore dorso-proximally rather than proximally widely separated, connected distally by sigmoidal fold. Ventral edge straight to slightly convex, tentacle notch not visible in external view.

Inner side of LAP with rather narrow, well-defined, finger-shaped, arched ridge, best defined and slightly widened at dorsal and ventral tips; dorsal tip of ridge rounded, pointing dorso-proximalwards; ventral tip sharply separated from thickened ventral edge of LAP; small, moderately well-defined, slightly prominent spur on inner side of ventro-distal tip of LAP; no other spur discernible on inner side of distal edge. Tentacle notch very large. No perforations discernible.

Paratype supplements and variation

NHMW 2012/0137/0002 is a dissociated median LAP of rectangular outline; dorsal edge strongly concave; ventro-distal tip of LAP slightly protruding; proximal edge of LAP slightly concave with moderately large, poorly defined, prominent spurs, one in the middle of the proximal edge, bluntly protruding, the second one close to the ventro-proximal tip of the LAP. Five spine articulations, similar to those of holotype. Ventral edge of LAP with large, but weakly concave tentacle notch.

Inner side similar to that of holotype.

NHMW 2012/0137/0003 is a dissociated distal LAP of rectangular outline; almost twice wider than high; dorsal edge slightly less concave than in holotype; ventral spur on proximal edge moderately well defined, prominent; no spur discernible in centre of proximal edge. Four spine articulations, similar to those of holotype. Ventral edge of LAP slightly concave; tentacle notch not visible in external view.

Inner side with narrow, bent, well-defined ridge; dorsal and ventral tips best defined and widest; dorsal tip pointing dorso-proximalwards; inner side of ventro-distal tip with large, prominent, well-defined, horizontally elongate spur; no other spur discernible on inner side of distal edge. Tentacle notch very large. No perforations visible.

Remarks

These LAPs display the highly distinctive combination of characters typically found in Eolaxoporus gen. nov., although the oblique spine articulations are unusual. Nevertheless, this LAP type appears best placed in Eolaxoporus gen. nov. and can be easily differentiated from its congeners on account of the oblique spine articulations and the very poorly developed spurs on the outer proximal and inner distal edges.

Occurrence

Late Sinemurian to early Pliensbachian of Austria.

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.