Inexpectacantha ritae, 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 : 186-187

Inexpectacantha ritae sp. nov.

urn:lsid:zoobank.org:act:7CCF96E7-E90E-4FD8-B307-1DEC45F8F82F

Fig. 33 : 1-3

Sigsbeia? lunaris – Thuy 2005: 41, pl. 4 figs 6-10 [material incorrectly assigned to Sigsbeia? lunaris ( Hess, 1962) ].

Diagnosis

Species of Inexpectacantha with moderately large LAPs; outer surface with finely meshed stereom, devoid of constriction, furrow or depressed area along proximal edge; up to six moderately large spine articulations in shallow notches of bulging distal portion, slightly oblique in proximal LAPs, more strongly oblique in median and distal ones; ridge on inner side LAP relatively slender, strongly bent dorso-proximalwards.

Etymology

Species named in honour of Rita Hellers, who gave me life and all the prerequisites to fill it with happiness, love and fulfilment.

Type material

Holotype

MnhnL HE419 .

Paratypes

MnhnL HE420 and MnhnL HE421.

Type locality and horizon

Bourglinster, Luxembourg; sample Bou of Thuy (2005), Planorbis Zone, Hettangian, Early Jurassic.

Additional material

MnhnL HE422 (55 dissociated LAPs) from sample Bou of Thuy (2005) from the Hettangian of Bourglinster, Luxembourg; MnhnL HE423 (16 dissociated LAPs) from sample Van1 of Thuy (2005)

from the Hettangian of Vance, Belgium; MnhnL HE254 (5 dissociated LAPs), MnhnL HE424 (20 dissociated LAPs) from sample Van2 of Thuy (2005) from the Hettangian of Vance, Belgium.

Description

Holotype

MnhnL HE419 is a dissociated, moderately large, proximal LAP; almost twice higher than wide; of massive and stout aspect; dorsal edge weakly convex, oblique; distal edge convex; proximal edge concave, devoid of spurs; no constriction or furrow along proximal edge; outer surface with moderately finely meshed stereom becoming slightly more finely meshed close to proximal edge of LAP. Six moderately large, ear-shaped, oval, horizontally slightly elongate, weakly oblique spine articulations in shallow notches of bulging distal portion of LAP; notches of three ventral spine articulations merged; spine articulations not sharply bordered proximally, edge of notches gentle; ventral lobe of spine articulations thin, rugged, confluent with stereom of notch and merged proximally with larger, thicker and more prominent dorsal lobe into continuous volute; strong dorsalward increase in size of gaps separating spine articulations; dorsalward increase in size of spine articulations very weak; gap between spine articulations and distal edge of LAP narrow. Ventral edge of LAP oblique, slightly convex; tentacle notch invisible in external view.

Inner side of LAP with large, moderately well-defined, prominent, relatively slender, dorso-proximalwards bent, tongue-shaped ridge devoid of kinks or strongly widened parts; ventral tip of ridge not merged with ventral portion of LAP; no spurs on inner side of distal edge of LAP; inner side of tentacle notch very small, poorly defined, shallow. No perforation or furrow discernible.

Paratype supplements and variation

MnhnL HE420 is a dissociated median LAP; slightly higher than wide; very well in agreement with holotype, of slightly more rounded aspect. Five spine articulations similar to those observed on holotype but more strongly oblique; weaker dorsalward increase in size of gaps separating spine articulations; two ventralmost spine articulations in very shallow notches, remaining ones freestanding.

Inner side similar to that of holotype.

MnhnL HE421 is a dissociated distal LAP; slightly higher than wide. Four spine articulations similar to those of holotype but more strongly oblique, almost vertical; weaker dorsalward increase in size of gaps separating spine articulations; two ventralmost spine articulations in very shallow notches, remaining two freestanding.

Inner side similar to that of holotype.

Remarks

These LAPs from the Hettangian of Luxembourg were originally recorded by Thuy (2005), along with conspecific LAPs from the Hettangian of Belgium, and erroneously assigned to Sigsbeia ? lunaris ( Hess, 1962) . While it is clear from the highly distinctive combination of characters that these LAPs are assignable to Inexpectacantha , the type specimens of Sigsbeia ? lunaris differ from the LAPs described above in the more strongly oblique spine articulations even in proximal LAPs, the presence of a slightly depressed band along part of the proximal edge, and the much wider and less strongly bent ridge on the inner side. Evidently, these LAPs are incompatible with any currently known LAP type assignable to Inexpectacantha and are thus described here as a new species.

Occurrence

Hettangian of Luxembourg and Belgium.

Figures

Fig. 33. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-3. Inexpectacantha ritae sp. nov. from the Hettangian (Early Jurassic) of Bourglinster, Luxembourg. 1. MnhnL HE419 (holotype), proximal LAP. 2. MnhnL HE420 (paratype), median LAP. 3. MnhnL HE421 (paratype), distal LAP. 4-6. Inexpectacantha weisi sp. nov. from the Hettangian (Early Jurassic) of Fontenoille, Belgium. 4. MnhnL HE425 (holotype), proximal LAP. 5. MnhnL HE426 (paratype), median LAP. 6. MnhnL HE427 (paratype), distal LAP. 7-8. Inexpectacantha lunaris (Hess, 1962) comb. nov. from the late Sinemurian (Early Jurassic) of Bishop’s Cleeve, Great Britain. 7. GZG. INV.78752, proximal LAP. 8. GZG.INV.78753, proximal to median LAP. 9-10. Inexpectacantha acrobatica Thuy, 2011 from the early Pliensbachian (Early Jurassic) of Blockley, Great Britain (9) and the early Toarcian (Early Jurassic) of Aix-sur-Cloie, Belgium (10). 9. GZG.INV.78755, proximal LAP. 10. GZG.INV.78757, juvenile proximal LAP. One common scale bar per species.