Ophiojagtus acklesi, 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 : 219-220

Ophiojagtus acklesi sp. nov.

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Fig. 38 : 5-7

Diagnosis

Ophiacanthid with stout, thick, strongly curved LAPs generally with a high height/width ratio; outer surface devoid of ornamentation elements; no spurs on outer proximal and inner distal edges; ventral portion of LAPs long to extremely long, strongly protruding ventralwards and often with widened ventral tip; proximal edge commonly with proximalwards pointing protrusion; large, ear-shaped spine articulations composed of thick, continuous volute, freestanding on bulging distal portion of LAP and not bordered proximally by a ridge-like structure; broad, well defined ridge on the inner side of the LAPs, generally with dorso-proximalwards pointing dorsal part; tentacle notch large but poorly defined and generally shallow.

Etymology

Species named in honour of Texas-born actor Jensen Ackles; my wife urged me to do so.

Type material

Holotype GZG.INV.78814 .

Paratypes

GZG.INV.78815 and GZG.INV.78816.

Type locality and horizon

Wizard Way, Texas, USA; echinoid marker bed of Smith & Rader (2009), latest Aptian, Early Cretaceous.

Additional material

GZG.INV.78817 (67 dissociated LAPs).

Description

Holotype

GZG.INV.78814 is a dissociated, moderately large, proximal LAP; approximately twice higher than wide; of stout, massive and strongly curved aspect; dorsal edge slightly concave on account of the pointed dorso-proximal tip of the LAP strongly protruding towards arm midline; distal edge convex; proximal edge concave, with two closely spaced, pointed protrusions, ventral one of which larger; ventral portion rather narrow and very long, accounting for more than one-third of the total LAP height, with widened, conspicuously ventro-proximalwards pointing ventral tip; outer surface with finely meshed stereom, devoid of ornament elements; slightly more coarsely meshed stereom on ventral portion of LAP. Four large, nearly equi-distant, ear-shaped spine articulations freestanding on strongly bulging distal portion of LAP, and composed of a thick, continuous volute; slight dorsalward increase in size of spine articulations; gap between spine articulations and distal edge of LAP rather narrow.

Inner side of LAP with well-defined, prominent, broad but very short, oblique ridge; dorsal tip of ridge strongly widened and ventro-proximalwards extending onto inner side of protrusions of proximal edge of LAP; ridge restricted to the centre of the inner side, no part of the ridge extending onto the ventral portion of the LAP; no spurs on the inner side of the distal edge of the LAP; inner side of the tentacle notch relatively large, very poorly defined, shallow, almost indiscernible. Single small perforation between tentacle notch and ventral tip of ridge.

Paratype supplements and variation

GZG.INV.78815 is a dissociated median to distal LAP; approximately 1.5 times higher than wide; very well in agreement with holotype; ventral portion accounting for almost half of the total LAP height; single, large, well-developed, round protrusion on proximal edge. Four spine articulations similar to those observed on holotype.

Inner side of LAP very well in agreement with that of holotype; ridge slightly shorter.

GZG.INV.78816 is a dissociated proximal LAP; ventral portion missing; single large, well-developed, rounded protrusion on proximal edge. Five spine articulations similar to those of holotype but with weaker dorsalward increase in size.

Inner side similar to that of holotype.

Remarks

The highly distinctive combination of characters displayed by these LAPs unambiguously places them in the genus Ophiojagtus gen. nov. Confusion with other LAP types assigned to this genus is precluded by the presence of four to five spine articulations, in combination with a very long ventral portion and a very short ridge on the inner side not extending onto the ventral portion of the LAP but with a strongly widened dorsal tip projecting onto the inner side of the well-developed protrusion of the proximal LAP edge. Since this LAP type displays the diagnostic combination of characters of Ophiojagtus gen. nov. most clearly, it is chosen as the type species of the genus.

Occurrence

Latest Aptian of Texas.

Figures

Fig. 38. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-4. Ophiojagtus irimurai gen. et sp. nov. from the early Kimmeridgian (Late Jurassic) of the Pointe du Chay, France. 1. GZG.INV.78808 (holotype), proximal LAP. 2. GZG.INV.78809 (paratype), median LAP. 3. GZG.INV.78810 (paratype), median LAP. 4. GZG.INV.78811 (paratype), distal LAP. 5-7. Ophiojagtus acklesi gen. et sp. nov. from the late Aptian (Early Cretaceous) of Wizard Way, Texas. 5. GZG.INV.78814 (holotype), proximal LAP. 6. GZG.INV.78815 (paratype), median to distal LAP. 7. GZG.INV.78816 (paratype), proximal LAP. 8. Ophiojagtus sp. 1 from the early Cenomanian (Late Cretaceous) of Waco, Texas; proximal LAP. 9-10. Ophiojagtus alternatus (Kutscher & Jagt, 2000) comb. nov. from the early late Maastrichtian (Late Cretaceous) of Haccourt, Belgium. 9. NHMM 2012 060, proximal to median LAP. 10. NHMM 2012 061, proximal LAP. One common scale bar per species.