Lapidaster caeloscopus, 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 : 28-30

Lapidaster caeloscopus sp. nov.

urn:lsid:zoobank.org:act:C670AEE6-65DA-49F5-B098-A8E1E372063A

Fig. 7 : 1-3

Diagnosis

Species of Lapidaster with small, elongate LAPs of trapezoid outline, well-developed constriction and strongly enlarged dorsalmost spine articulation pointing dorsally.

Etymology

Name composed of caelum, Latin for “sky”, and scopus, Latin for “target”, in reference to the large, dorsally pointing, or “skygazing”, dorsalmost arm spine articulation in this species.

Type material

Holotype

NHMW 2012/0137/0005 .

Paratypes

NHMW 2012/0137/0006 and NHMW 2012/0137/0007.

Type locality and horizon

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

Additional material

NHMW 2012 /0137/0008 (12 dissociated LAPs).

Description

Holotype

NHMW 2012 /0137/0005 is a dissociated, very small, proximal LAP, somewhat wider than high, of irregularly rectangular to trapezoid outline, with slightly concave dorsal edge as a result of a weak constriction; slightly concave distal edge; ventral fifth of LAP protruding ventro-proximalwards; ventrodistal tip of LAP very large, tongue shaped, strongly protruding ventro-distalwards; proximal edge of LAP almost straight to slightly concave, except for sharp kink in ventral quarter; the latter ventrally bordered by well-defined, elongate, lens-shaped and strongly prominent spur; outer surface with finely to moderately coarsely meshed stereom, with trabeculae not merged into vertical striation. Three earshaped spine articulations; conspicuously wide gap between spine articulations and distal edge of LAP; very strong dorsalward increase in size of spine articulations; dorsalmost spine articulation more than twice larger than ventralmost one, conspicuously pointing dorsalwards; dorsal and ventral lobes of spine articulations forming continuous volute; dorsal gap between spine articulations slightly larger than ventral one. Ventral edge of LAP with very large, concave tentacle notch.

Inner side of LAP unfortunately partially obscured by sediment; ridge discernible, well defined, prominent, nearly straight to slightly bent, narrow, small and conspicuously short, hardly reaching horizontal midline of LAP, ventral tip of ridge well defined, not merged with slightly thickened ventral part of LAP; inner side of ventro-distal tip of LAP thickened into large, prominent, elongate and slightly protruding spur composed of dense stereom. Inner side of large tentacle notch obscured by sediment; presence of possible perforations on inner side indeterminable.

Paratype supplements and variation

NHMW 2012 /0137/0006 is a dissociated median LAP, approximately twice wider than high, of trapezoid outline; ventro-distal tip of LAP very large and strongly protruding; dorsal edge clearly concave as a result of the constricted outer surface; distal edge oblique, straight to slightly convex; dorsal four-fifths of proximal edge evenly convex; ventral fifth of proximal edge separated from the latter by sharp kink, ventrally bordered by moderately well-defined, prominent, elongate spur. Three spine articulations; dorsalward increase in size much weaker than in holotype; dorsalmost spine articulation slightly larger than remaining two, pointing dorsalwards; conspicuously wide gap between row of spine articulations and distal edge of LAP, as in holotype. Ventral edge of LAP with very large, gently concave tentacle notch.

Inner side of LAP largely obscured by sediment; ridge similarly short as in holotype; inner side of ventro-distal tip of LAP with large, oval, strongly prominent spur composed of dense stereom.

NHMW 2012 /0137/0007 is a dissociated distal LAP, more than twice wider than high, with strongly concave dorsal edge indicating a strong constriction; proximal edge undulose, with central convex part and ventral quarter sharply separated by kink; the latter bordered by relatively large, yet poorly defined, elongate, prominent spur. Two spine articulations, one near the ventral edge of the LAP, the second in the middle of the LAP, slightly larger than the ventral one. Ventral edge of LAP almost straight, except for large, yet only weakly concave tentacle notch.

Inner side with very small, short, knob-like, prominent and well-defined ridge, widest ventrally and not merged with ventral part of LAP.

Remarks

The very small, dissociated LAPs of Lapidaster caeloscopus sp. nov. are unique in displaying a strongly enlarged dorsalmost spine articulation which points dorsally. The irregular trapezoid outline of the LAPs, as well as the very short ridge on the inner side, are further characters which clearly set the LAPs of L. caeloscopus sp. nov. apart from any other known type of LAPs. Greatest similarities are shared with the LAPs of Lapidaster lukenederi sp. nov. (see below) from the Valanginian of Austria, especially on account of the constriction, the rather thin plate architecture, the small size, and the height/width ratio of the proximal LAPs, which is indicative of elongated arm segments, a typically paedomorphic character ( Stöhr 2005). In contrast, similarities to the distal LAPs of Reitneracantha dissidens sp. nov., which occur in the same samples, are merely superficial and limited to the enlarged dorsally pointing spine articulations found in both species. Almost all other characters, in particular the development of the tentacle notch, the outer surface ornamentation and the morphology of the spine articulations clearly differ in both species.

Assignment to Lapidaster gen. nov. is suggested here on account of the general Ophiologimus -like LAP morphology (very large tentacle notch, ventro-proximalwards protruding ventral portion of LAP, strongly protruding ventro-distal tip of LAP, spine articulations neither sunken in depressions nor positioned on strongly elevated ridge), combined with the presence of a well-developed spur on the outer proximal and inner distal edges of the LAP.

Occurrence

Late Sinemurian to early Pliensbachian of Austria.

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.