Sabinacantha archetypa, 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 : 207-208

Sabinacantha archetypa sp. nov.

urn:lsid:zoobank.org:act:6CDF4231-69E4-419E-8596-AA9BDE71DC3C

Fig. 36 : 6-8

Diagnosis

As for genus.

Etymology

Name formed after archetypum, Latin for “archetype” or “idol”, referring to the precursor state of the species in the Sabinacantha - Ophiohamus lineage.

Type material

Holotype GZG.INV.78771 .

Paratype

GZG.INV.78772 and GZG.INV.78773.

Type locality and horizon

Plettenberg near Balingen, Germany; clay pockets between sponge associations in the lowest bed exposed in the quarry, Bimammatum Zone, late Oxfordian, Late Jurassic.

Additional material

GZG.INV.78774 (3 dissociated LAPs).

Description

Holotype

GZG.INV.78771 is a dissociated, moderately large, proximal LAP; thick, massive, rounded aspect; slightly higher than wide; dorsal edge and dorsal half of distal edge evenly convex, not separated by kink; ventral half of distal edge slightly concave; proximal edge convex, with small, moderately well-defined, rounded, prominent and very weakly protruding spur; ventro-proximal tip of LAP protruding; outer surface with coarse, irregular vertical striation composed of thick, non-overlapping lamellae replaced by moderately finely meshed stereom in proximal quarter of outer surface, with ventro-proximalward fining of stereom. Three small, ear-shaped, equi-distant, oval, horizontally slightly elongate spine articulations freestanding on very weakly elevated ventral third of otherwise striated distal edge of LAP; weak dorsalward decrease in size of spine articulations; dorsal and ventral lobes of spine articulations separated by small notch proximally; spine articulations sharply bordered proximally by lamella of outer surface striation. Ventral edge of LAP convex, no tentacle notch discernible.

Inner side of LAP with large, short, very broad, well-defined, uniformly prominent ridge; ventral part of ridge narrowest, pointing ventralwards, not merged with ventral portion of LAP; dorsal part of ridge strongly widened, rounded, pointing dorso-proximalwards; inner side of distal edge of LAP with moderately large, round, well-defined, very weakly prominent spur composed of densely meshed stereom; inner side of tentacle notch small, well defined laterally, slightly oblique. No perforations or furrow discernible.

Paratype supplements and variation

GZG.INV.78772 is a dissociated median LAP; nearly as high as wide; well in agreement with holotype; part of proximal edge with spur strongly protruding; spur itself poorly defined, almost indiscernible; vertical striation on outer surface less well developed and less regular than in holotype, replaced by coarsely meshed stereom on most of the outer surface except near the spine articulations and in the ventro-proximal area of finely meshed stereom. Three spine articulations similar to those observed on holotype but on weakly elevated ventral half (rather than third) of distal LAP edge.

Inner side similar to that of holotype. Group of very small, irregular perforations dorsally bordering tentacle notch.

GZG.INV.78773 is a dissociated distal LAP; slightly wider than long; spur on proximal edge of LAP moderately well defined, strongly protruding, composed of densely meshed stereom; ventro-proximal tip of LAP strongly oblique; outer surface ornament as in holotype. Three spine articulations similar to those observed on holotype but on ventral half rather than third of distal edge of LAP.

Inner side of LAP similar to that of holotype; ridge slightly shorter; spur on inner side of distal edge slightly larger, less well defined.

Remarks

These LAPs are the only ones assigned to Sabinacantha gen. nov. For a discussion of their taxonomic affinities, reference is made to the section “Remarks” of the genus.

Occurrence

Late Oxfordian of Germany.

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.