Lapidaster fasciatus ( Kutscher & Villier, 2003 ) 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 : 32-34

Lapidaster fasciatus ( Kutscher & Villier, 2003) comb. nov.

Fig. 7 : 7-8

Sinosura fasciata Kutscher & Villier, 2003: 185 , pl. 3 fig. 9, pl. 4 figs 1-2.

Sinosura schneideri – Kutscher 1996: p. 9, pl. 2 figs 6-8 (material incorrectly assigned to Sinosura schneideri Kutscher, 1987 ).

Diagnosis

Species of Lapidaster gen. nov. with small- to medium-sized LAPs displaying an irregular, coarse vertical striation, a relatively short ridge on the inner side, and up to four spine articulations composed of confluent dorsal and ventral lobes.

Material examined

GZG. INV.78505, GZG. INV.78506 and GZG. INV.78507-1 (16 dissociated LAPs) from the Middle Toarcian of Le Clapier, France; GZG. INV.78507-2 (8 dissociated LAPs) from the Causses, France; type material of Kutscher & Villier (2003) from the late Toarcian of Sainte-Verge, France; original material of Kutscher (1996) from the Toarcian/Aalenian of Quedlinburg, Germany.

Description

Relatively small LAPs, proximal ones slightly higher than wide, median ones slightly wider than high and distal ones nearly twice wider than high, with gently convex distal edge; dorsal edge slightly convex (proximal LAPs) to slightly concave (distal LAPs); ventral fifth to quarter of LAP protruding ventroproximalwards; ventro-distal tip of LAP pointed, protruding; proximal edge irregularly concave, with poorly (in proximal LAPs) to well-defined (in distal LAPs), obliquely elongate, slightly prominent spur near ventro-proximal tip, composed of slightly denser stereom; outer surface with coarsely meshed stereom, with trabeculae merging into irregular but well-developed vertical striation. Three (distal LAPs) to four (proximal LAPs) moderately large, ear-shaped spine articulations, with dorsal and ventral lobes forming continuous volute; dorsalward increase in size of spine articulations, with dorsalmost one, however, smaller than second dorsalmost; dorsalward increase in size of gaps separating spine articulations; two to three ventral spine articulations separated from striated outer surface by irregular, confluent areoles of slightly more finely meshed stereom; dorsalmost spine articulation embedded in striated outer surface. Ventral edge of LAP with large, deeply concave tentacle notch.

Inner side of LAP with sharply defined, rather narrow ridge, dorsal portion of which oblique and slightly bent, not widened dorsally and not approaching dorsal or proximal edges of LAP; ventral portion of ridge separated from dorsal one by slightly rounded kink, very short, rapidly merging into thickened ventral part of LAP; inner side of ventro-distal tip of LAP with small, moderately well-defined, slightly prominent spur. Inner side of large tentacle notch with coarsely reticulate, horizontally stretched stereom.

Remarks

These LAPs seem to be identical with those described and illustrated by Kutscher (1996) from the Toarcian and Aalenian of Germany and assigned to Sinosura schneideri Kutscher, 1987 . Similar LAPs from the Toarcian of France have subsequently been described by Kutscher & Villier (2003), who reassigned them to their new species Sinosura fasciata Kutscher & Villier, 2003 . The genus Sinosura Hess, 1964 was introduced by Hess (1964) to accommodate fossil ophiuroid species with fragile LAPs displaying a vertical striation, a wide gap between the spine articulations and the distal edge of the LAP and well-developed spine articulations. Superficially, the LAPs described by Kutscher (1996) and Kutscher & Villier (2003) fit this diagnosis. However, an examination of the type material of Sinosura brodiei (Wright, 1866) , the type species of the genus, from the Pliensbachian of Great Britain, as well as of additional, exceptionally well-preserved material from the Pliensbachian of France (Thuy et al. 2011) has revealed a fundamental difference in spine articulation morphology. While the spine articulations in S. brodiei are of the ophioleucinid type as described by Martynov (2010), those of S inosura fasciata are ear-shaped with a sigmoidal fold, as typically found in the Ophiacanthidae ( Martynov 2010) . On the basis of the clearly ophiacanthid spine articulation structure in combination with the generally Ophiologimus -like morphology and the presence of a spur on the outer proximal and inner distal edges, Sinosura fasciata is here transferred to Lapidaster gen. nov.

Lapidaster fasciatus comb. nov. differs from L. hystricarboris sp. nov. and L. wolfii sp. nov. in displaying a much lower number of spine articulations. Lapidaster lukenederi sp. nov. and L. etteri sp. nov. both have constricted LAPs in contrast to L. fasciatus comb. nov., and in L. coreytaylori sp. nov. the trabeculae of the outer surface stereom are very thick and not merged into vertical stripes. Greatest similarities are shared with L. mastodon sp. nov. and L. varuna sp. nov. In the former, however, the LAPs have a much less strongly protruding ventro-distal tip, generally no more than three spine articulations, separated ventral and dorsal lobes of the spine articulations, and a more rounded overall aspect. In L. varuna sp. nov., the ridge on the inner side of the LAP is longer, and the vertical striation on the outer surface is much less developed.

Occurrence

Middle and Late Toarcian of France; Toarcian/Aalenian of Germany.

Figures

Fig. 7. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-3. Lapidaster caeloscopus gen. et sp. nov. from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 1. NHMW 2012/0137/0005 (holotype), proximal LAP. 2. NHMW 2012/0137/0006 (paratype), median LAP. 3. NHMW 2012/0137/0007 (paratype), distal LAP. 4-6. Lapidaster hystricarboris gen. et sp. nov. from the early Pliensbachian (Early Jurassic) of Blockley, Great Britain. 4. GZG.INV.78501 (holotype), proximal LAP. 5. GZG.INV.78502 (paratype), median LAP. 6. GZG.INV.78503 (paratype), distal LAP. 7-8. Lapidaster fasciatus (Kutscher & Villier, 2003) comb. nov. from the middle Toarcian (Early Jurassic) of Le Clapier, France. 7. GZG.INV.78505, proximal LAP. 8. GZG.INV.78506, distal LAP. One common scale bar per species is given.