Inexpectacantha weisi, 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 : 189-190

Inexpectacantha weisi sp. nov.

urn:lsid:zoobank.org:act:96A19195-86C6-4EA8-B6F2-AEDA14589A66

Fig. 33 : 4-6

Hemieuryale ? n. sp. – Kutscher & Hary 1991: 54, pl. 2 fig. 4a-d.

Diagnosis

Species of Inexpectacantha with small LAPs displaying a coarsely meshed stereom on the outer surface; no constriction and no furrow along proximal edge; spine articulations freestanding, not in depressions, oblique; single spine articulation with lip-shaped distal knob.

Etymology

Species named in honour of my friend and colleague Robert Weis for his continuous encouragement and for digging up the type locality of the species.

Type material

Holotype

MnhnL HE425 .

Paratypes

MnhnL HE426 and MnhnL HE427.

Type locality and horizon

Fontenoille, Belgium; level c of Delsate et al. (2002), Liasicus Zone, Hettangian, Early Jurassic.

Additional material

MnhnL HE428 (81 dissociated LAPs) from the Hettangian of Fontenoille, Belgium; MnhnL HE429 (28 dissociated LAPs) from the Bucklandi Zone, early Sinemurian of Remerschen, Luxembourg.

Description

Holotype

MnhnL HE425 is a dissociated, small, proximal LAP; slightly higher than wide; of thick, massive and rounded aspect; dorsal edge oblique but straight; distal edge convex; proximal edge nearly straight, devoid of spurs; outer surface with moderately coarsely meshed stereom, except for poorly defined, weakly sunken area of finely meshed stereom near ventro-proximal tip of LAP; no vertical striation or other conspicuous ornament elements. Five small, ear-shaped, oblique spine articulations freestanding on bulging distal portion of LAP, not sharply separated proximally from outer surface stereom and not sunken; ventral lobe rugged, thin, merged proximally with much thicker, smoother and more prominent dorsal lobe into continuous volute; weak dorsalward increase in size of spine articulations but not in size of gaps separating them; gap between spine articulations and distal edge almost as wide as one spine articulation. Ventral edge of LAP oblique, weakly convex; tentacle notch invisible in external view.

Inner side of LAP with very large, broad, conspicuous, well-defined, prominent, strongly dorsoproximalwards bent, tongue-shaped ridge; dorsal part of ridge wider than ventral one; ventral tip of ridge not merged with ventral portion of LAP; no spur on inner side of distal edge of LAP; inner side of tentacle notch very small, shallow and poorly defined. Very poorly defined, shallow, almost indiscernible vertical furrow dorsally bordering tentacle notch; no perforations discernible.

Paratype supplements and variation

MnhnL HE426 is a dissociated median LAP; slightly wider than high; very well in agreement with holotype; outer surface better preserved, with coarsely meshed stereom devoid of vertical striation or granules; narrow and of more finely meshed stereom along proximal edge increasing in width ventralwards. Four equi-distant spine articulations similar to those observed on holotype but better preserved; strong dorsalward increase in size of spine articulations; gap between spine articulations and distal edge of LAP narrower.

Inner side of LAP well in agreement with that of holotype.

MnhnL HE427 is a dissociated distal LAP; approximately 1.5 times wider than high; dorsal edge straight, weakly oblique; proximal edge irregularly concave. Four spine articulations similar to those observed on holotype except for ventralmost one with small, lip-shaped, strongly protruding distal knob; dorsalward increase in size of spine articulations and of gaps separating them; gap between spine articulations and distal edge of LAP narrower than in holotype. Ventral edge of LAP slightly convex.

Ridge on inner side of LAP smaller, narrower and less clearly tongue shaped than in holotype, with pointed dorsal tip and distally bordered by small, poorly defined knob.

Remarks

These LAPs are unambiguously assignable to Inexpectacantha on account of the stout, thick, rounded general aspect, the lack of outer surface ornament and spurs, the shape, size and position of the spine articulations and the shape of the ridge on the inner side. Within this genus, greatest similarities are shared with the LAPs of Inexpectacantha acrobatica , especially with respect to the freestanding spine articulations. The LAPs described above, however, lack a constriction or a furrow along the proximal edge, and display a more coarsely meshed stereom on the outer surface and fewer spine articulations.They are thus here described as a new species. The strongly prominent, lip-shaped knob on the ventralmost spine articulation in the distal LAP noted above most probably bore a hook-shaped spine similar to those known from the type material of I. acrobatica (see Thuy 2011).

Kutscher & Hary (1991) described and illustrated dissociated LAPs from the Sinemurian of Luxembourg as “ Hemieuryale ? n. sp.”, recognising the species as new but refraining from formally naming it on account of the limited amount of material available. The specimens in question appear to be conspecific with the LAPs described here, although only some of the original specimens of Kutscher & Hary (1991) could be examined by myself. The material from the Pliensbachian of Great Britain described as Hemieuryale ? lunaris Hess, 1962 by Hess (1964) was considered by Kutscher & Hary (1991) to be conspecific with their unnamed LAPs. As shown below, however, Hess’s (1964) original assignment was correct.

Occurrence

Hettangian of Belgium, early Sinemurian of Luxembourg.

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.