Reitneracantha dissidens, 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 : 204-206

Reitneracantha dissidens sp. nov.

urn:lsid:zoobank.org:act:E1A8998E-30EE-4921-B054-371C65DB6C9D

Fig. 36 : 1-3

Diagnosis

As for genus.

Etymology

From dissidere, Latin for “intractable, dissenting with an established policy”, in reference to the fact that this species challenges established concepts of the role of the deep-sea in macroevolutionary patterns.

Type material

Holotype

NHMW 2012/0137/0029 .

Paratypes

NHMW 2012/0137/0030 and NHMW 2012/0137/0031.

Type locality and horizon

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

Additional material

NHMW 2012/0137/0032 (3 dissociated LAPs).

Description

Holotype

NHMW 2012/0137/0029 is a dissociated, moderately large, proximal LAP; dorsal edge nearly straight, oblique; distal edge convex; proximal edge nearly straight, except for small, very poorly defined, almost indiscernible, weakly prominent and protruding spur; outer surface with finely meshed stereom, devoid of conspicuous ornament. Five large, ear-shaped spine articulations freestanding on strongly elevated distal half of LAP; dorsal edge of spine articulations vertically elongated, with conspicuous central notch, much larger than ventral lobe, merged with the latter into continuous volute; very strong dorsalward increase in size of spine articulations and of gaps separating them; dorsalmost spine articulation largest, well below dorsal edge of LAP, comspicuously dorsalwards pointing; proximal edge of spine articulations irregularly corrugated; spine articulations sharply bordered proximally by edge of elevated portion, except for dorsalmost one; gap between spine articulations and distal edge of LAP as wide as one spine articulation. Ventral edge of LAP nearly straight; tentacle notch invisible in external view.

Inner side of LAP with small, sharply defined, prominent, gently bent ridge displaying a ventroproximally bent ventral part not merged with ventral portion of LAP, and a widened, angular dorsal tip; inner side of distal edge of LAP devoid of spurs; inner side of tentacle notch small, well defined laterally, semi circular. No perforations or furrow discernible.

Paratype supplements and variation

NHMW 2012/0137/0030 is a dissociated median LAP; as high as wide; of rectangular to trapezoid aspect; dorsal edge concave as a result of a constriction; distal edge nearly straight, oblique; proximal edge devoid of spurs. Four spine articulations similar to those observed on holotype; dorsalmost spine articulation much larger than remaining ones and widely separated from the latter, dorsalwards pointing, near dorsal edge of LAP. Ventral edge of LAP straight, no tentacle notch visible.

Ridge on inner side of LAP similar to that of holotype but with less strongly widened dorsal tip.

NHMW 2012/0137/0031 is a dissociated distal LAP; slightly wider than high; dorsal edge strongly concave as a result of a well-developed constriction; proximal edge gently concave, devoid of spurs. Four spine articulations similar to those of holotype, freestanding on slightly elevated distal third of LAP; dorsalmost spine articulation much larger than remaining ones and widely separated from the latter, pointing dorsalwards, at some distance from the dorsal edge of the LAP. Ventral edge of the LAP concave, no tentacle notch visible in external view.

Ridge on inner side of LAP similar to that of holotype but with weakly widened dorsal tip; inner side of distal edge of LAP devoid of spurs; inner side of tentacle notch moderately small, well defined laterally, semi circular.

Remarks

The taxonomic affinities of these LAPs have been discussed above.

Figures

Fig. 36. Lateral armplates (LAPs) of fossil and Recent ophiacanthidbrittle stars in external (a) and internal (b) views. 1-3. Reitneracantha dissidens gen. et sp. nov. from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 1. NHMW 2012/0137/0029 (holotype), proximal LAP. 2. NHMW 2012/0137/0030 (paratype), median LAP. 3. NHMW 2012/0137/0031 (paratype), distal LAP. 4-5. Ophiohamus nanus O’Hara & Stöhr, 2006, Recent. 4. Proximal to median LAP. 5. Proximal to median LAP. 6-8. Sabinacantha archetypa gen. et sp. nov. from the late Oxfordian (Late Jurassic) of the Plettenberg, Germany. 6. GZG.INV.78771 (holotype), proximal LAP. 7. GZG.INV.78772 (paratype), median LAP. 8. GZG.INV.78773 (paratype), distal LAP. One common scale bar per species.