Eolaxoporus hagdorni, 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 : 22-25

Eolaxoporus hagdorni sp. nov.

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Fig. 6 : 2-4

Diagnosis

Species of Eolaxoporus gen. nov. with small LAPs displaying a low height/width ratio; two moderately well-defined spurs on outer proximal and inner distal edges, close to dorsal and ventral edges, respectively; up to four near-horizontal spine articulations; ridge on inner side relatively short and wide.

Etymology

Named in honour of Hans Hagdorn, who generously provided most of the Triassic samples used in the present study, including those that yielded the type material of the present species.

Type material

Holotype

MHI 2084/1 .

Paratypes

MHI 2085/1 and MHI 2086/1.

Type locality and horizon

Jushui, Sichuan, China; marly beds in the upper Hanwang Formation, late Carnian, Late Triassic.

Additional material

MHI 2087/1-35 (35 dissociated LAPs from sample C30); MHI 2088/1-11 (11 dissociated LAPs from sample C36); MHI 2089/1 (1 dissociated LAP from sample C33).

Description

Holotype

MHI 2084/1 is a dissociated, small, proximal LAP of rectangular outline; slightly wider than high; dorsal edge strongly concave as a result of a well-developed constriction; ventral fifth of LAP very weakly protruding ventro-proximalwards; ventro-distal tip of LAP protruding; distal edge straight to slightly concave; proximal edge with central notch and two large, moderately well-defined, slightly prominent yet strongly protruding spurs, one in the middle of the dorsal half of the proximal edge, the second in the middle of the ventral half; outer surface lacking conspicuous ornamentation; stereom of outer surface coarsely meshed in a vertical band along the midline of the LAP, becoming more finely meshed towards the proximal edge and towards the spine articulations. Four ear-shaped spine articulations on elevated distal part of LAP; slight dorsalward increase in size of spine articulations and in size of gaps separating them; dorsal and ventral lobes of spine articulations nearly parallel, horizontally elongate, separated proximally by small knobs, connected distally by sigmoidal fold. Ventral edge of LAP with large, concave tentacle notch.

Inner side of LAP with large, prominent, sharply defined, relatively short, tongue shaped, arched ridge; dorsal tip of ridge round, not widened, pointing dorso-proximalwards; ventral tip of ridge widest, sharply defined rather than merged with ventral edge of LAP; inner side of distal edge with two large, well-defined, prominent but not protruding spurs composed of slightly denser stereom, one near dorsodistal tip of LAP, the second near ventro-distal tip. Inner side of tentacle notch with coarsely meshed, slightly horizontally stretched stereom. No perforations discernible.

Paratype supplements and variation

MHI 2085/1 is a median dissociated LAP of rectangular outline; approximately 1.5 times wider than high; morphologically matching the holotype; spurs on proximal edge less well defined. Four nearly equal-sized spine articulations.

Inner side well in agreement with that of holotype; spurs on distal edge less well defined.

MHI 2086/1 is a dissociated distal LAP; twice wider than high; constriction less well developed than in holotype, thus distal part of LAP less strongly elevated; spurs on proximal edge almost indiscernible. Three nearly equal-sized spine articulations. Ventral edge of LAP with relatively large, gently concave tentacle notch.

Inner side with small, prominent, sharply defined, tongue-shaped knob; two large, poorly defined spurs composed of denser stereom on inner distal edge.

Remarks

These LAPs can be easily distinguished from the other LAP types assignable to Eolaxoporus n. gen. on account of the vertical spine articulations, in combination with a wide ridge on the inner side and two weakly protruding spurs, the dorsal one of which is close to the dorso-proximal tip of the LAP. It

displays the highly distinctive combination of characters of Eolaxoporus gen. nov. best and is thus here described as its type species.

Occurrence

Late Carnian of Sichuan, China.

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.