Lapidaster hystricarboris, 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 : 31-32

Lapidaster hystricarboris sp. nov.

urn:lsid:zoobank.org:act:FBF92066-FE54-4400-867E-FE2E3845307A

Fig. 7 : 4-6

Diagnosis

Species of Lapidaster gen. nov. with relatively large LAPs displaying a very finely striated outer surface and up to six spine articulations increasing in size dorsalwards.

Etymology

Name derived from Hystrix, a genus of porcupine, and arbor, Latin for “tree”, in honour of Steven Wilson, Richard Barbieri, Gavin Harrison and Colin Edwin of Porcupine Tree whose music was a fertile source of inspiration whenever the creative process of the present study threatened to come to a halt.

Type material

Holotype GZG.INV.78501 .

Paratypes

GZG.INV.78502 and GZG. INV.78503.

Type locality and horizon

Blockley, near Cheltenham, Great Britain; shell lenses in clay matrix, Davoei Zone, early Pliensbachian, Early Jurassic.

Additional material

GZG. INV.78504 (41 dissociated LAPs).

Description

Holotype

GZG.INV.78501 is a dissociated, medium-sized, proximal lateral arm plate, almost twice higher than wide, with rounded outline, ventral quarter of plate protruding ventro-proximalwards; conspicuous, tongue-like ventro-distal protrusion; dorsal edge of LAP strongly convex; proximal edge gently concave, with single poorly defined, slightly protruding spur close to ventro-proximal tip of the LAP, no other spurs discernible on outer proximal edge; distal edge gently convex; no constriction. Outer surface with irregular vertical striation consisting of very fine ridges separated by narrow bands of fenestrate stereom; ridges irregularly converging on ventral half of outer surface; striation rapidly grading into fine granulation followed by finely meshed stereom towards the proximal edge of the LAP; striation sharply separated from three ventralmost spine articulations, and confluent with the proximal edges of the three dorsal spine articulations, with conspicuous overlap of the striation onto the proximal edge of the dorsalmost spine articulation. Six large, ear-shaped spine articulations freestanding in continuous vertical row close to distal edge of LAP; dorsal and ventral lobes forming continuous volute; dorsalward increase in size of spine articulations and gaps separating them. Ventral edge of LAP with large, conspicuous, evenly concave tentacle notch.

Inner side of LAP with single thin, well-defined, prominent, oblique ridge, slightly widening towards its rounded dorsal tip; dorsal half of ridge nearly straight, not reaching dorsal or proximal edges of LAP, ventral half gently bent, poorly defined and confluent with thickened ventral quarter of LAP; irregular set of perforations on inner side of LAP, hardly discernible as vertical row corresponding to spine articulations; distal edge of LAP thinning distalwards; inner side of ventro-distal protrusion with well- defined, prominent knob, corresponding to poorly developed spur on outer proximal edge of the LAP. Inner side of tentacle notch with coarsely reticulate stereom reminiscent of horizontally stretched glue.

Paratype supplements and variation

GZG.INV.78502 is a dissociated median lateral arm plate, slightly higher than wide; overall morphology agreeing well with holotype. Dorsal edge nearly straight, ventro-distal tip of LAP hardly protruding; proximal edge of LAP strongly concave, with large, poorly defined and barely prominent and protruding spur near ventro-proximal tip of plate, and small, sharply defined, prominent and slightly protruding dorsal spur. Vertical striation on outer surface separated from three ventral spine articulations, confluent with proximal edge of two dorsal spine articulations. A total of five large spine articulations with clear dorsalward increase in size and gaps separating them. Dorsalmost spine articulation, as in holotype, with clear onlap of striation onto proximal edge.

Inner side of LAP in agreement with morphology of holotype; no perforations discernible. Very poorly defined, barely prominent spur in the centre of the inner distal edge of the LAP; spur on inner side of ventro-distal tip of LAP poorly developed, slightly prominent.

GZG.INV.78503 is a dissociated distal lateral arm plate, approximately 1.5 times wider than high. Dorsal edge oblique and straight to very gently convex; ventro-distal tip of LAP slightly protruding; proximal edge of LAP with very well-defined, prominent and clearly protruding spur in centre and second, poorly defined and slightly prominent spur close to ventro-proximal tip of LAP. Vertical striation on outer surface separated from three ventral spine articulations, slightly confluent with single dorsalmost spine articulation. A total of four, near-equal sized spine articulations, the dorsalmost separated from the remainder by a slightly larger gap. Inner side well in agreement with holotype. Two well-defined, prominent spurs on inner distal edge of LAP, corresponding to spurs on outer proximal edge. Single irregular perforation on inner side. Tentacle notch conspicuously large, very similar to notch observed in holotype.

Remarks

The large size of the LAPs of Lapidaster hystricarboris sp. nov. and their high number of spine articulations differentiaties them from almost all other LAP types assigned to this new genus. Greatest similarities are shared with the LAPs of Lapidaster wolfii sp. nov. In the latter, however, the spine articulations lack the dorsalward increase in size, and the vertical striation of the outer surface is very coarse, yet faint, in contrast to the well-developed, fine striation observed in L. hystricarboris sp. nov. There is a certain resemblance with the LAPs described as Ophiacantha ? rugosa Kutscher & Jagt, 2000 by Kutscher & Jagt (2000) from the early Maastrichtian of Germany and Denmark, and here re-assigned to Ophiologimus (see below). The LAPs of L. hystricarboris sp. nov., however, differ in displaying a spur on the outer proximal and inner distal edges, and in having a continuous ridge on the inner side rather than two separate knob-like structures. Lapidaster hystricarboris sp. nov. best exemplifies the great similarities, along with slight yet diagnostic differences, between Lapidaster gen. nov. and Ophiologimus , and is therefore chosen as the type species of the former.

Occurrence

Early Pliensbachian of Great Britain.

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.