Ophiotoma charlottae, 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 : 60-62

Ophiotoma charlottae sp. nov.

urn:lsid:zoobank.org:act:BFA9592E-7CEA-4B12-B2F0-45E1E27B7EF6

Fig. 12 : 8-10

Diagnosis

Species of Ophiotoma with comparatively small LAPs displaying a large, nearly rectangular and strongly protruding ventral portion (third of a proximal LAP); four to five equal-sized spine articulations; outer surface with striation restricted to relatively narrow band close to spine articulations and composed of thin lamellae separated by single rows of small stereom pores; inner side with main, central bone-shaped ridge and second ridge on ventral portion of LAP; very large, single perforation bordering ventral tip of main ridge, occasionally dorsally accompanied by second vertically elongate ridge.

Etymology

Species named in honour of Charlotte Bruneau for introducing me to Alexandre Jardin’s wonderful L’île des gauchers.

Type material

Holotype GZG.INV.78545 .

Paratypes

GZG.INV.78546 and GZG.INV.78547.

Type locality and horizon

Pointe du Chay near La Rochelle, France; Achilles Subzone, Cymodoce Zone , early Kimmeridgian, Late Jurassic.

Additional material

GZG.INV.78548 (3 dissociated LAPs).

Description

Holotype

GZG.INV.78545 is a dissociated, small, proximal LAP; approximately 1.5 times higher than wide; slightly convex dorsal and distal edges; proximal edge gently concave with very slight central protrusion; no spurs discernible on proximal edge; small, poorly defined, shallow depression in the middle of the proximal edge; ventral third nearly rectangular, strongly protruding ventro-proximalwards; no constriction; distal portion of LAP neither bulging nor elevated; outer surface with fine, regular vertical striation composed of thin lamellae separated by single rows of small stereom pores; striation replaced by finely meshed stereom in proximal third of outer surface and on most of the ventral portion of the LAP. Four ear-shaped, equal-sized spine articulations in shallow notches of the distal edge, moderately deeply incising the vertical striation of the outer surface; slight dorsalward increase in size of gaps separating the spine articulations; dorsal and ventral lobes separated by a small knob; almost no gap between spine articulations and distal edge of LAP. Ventral edge of LAP with very large, slightly angular tentacle notch.

Inner side of LAP with large but comparatively short, sharply defined, prominent, bone-shaped main ridge; dorsal portion of ridge oblique, with strongly widened dorsal tip; ventral portion with similarly widened ventral tip, well defined but not as sharply and prominently as dorsal tip; second less welldefined, less prominent but slightly wider, proximally bent ridge proximally bordering the inner side of the tentacle notch, in direct continuation of the ventral portion of the main ridge but separated from the latter; no spurs on the inner side of the distal edge of the LAP; inner side of the tentacle notch with coarsely meshed, horizontally stretched stereom, almost as wide as half of the total ventral LAP edge width. Single very large perforation distally bordering the tip of the ventral portion of the main ridge; second smaller, vertically elongate perforation above large one. Ventro-distal edge of ventral LAP portion with prominent ridge.

Paratype supplements and variation

GZG.INV.78546 is a proximal LAP; well in agreement with holotype. Vertical striation on outer surface extending to a slightly larger area close to spine articulations and on dorsal edge of ventral portion of LAP. Five spine articulations, of equal size and nearly equi-distant.

Inner side very well in agreement with that of holotype. Vertically elongate perforation lacking.

GZG.INV.78547 is a median LAP; nearly as high as wide; well in agreement with holotype; ventral quarter of LAP strongly protruding ventro-proximalwards; shallow, poorly defined depression in the centre of the proximal edge slightly larger. Five equal-sized, nearly equi-distant spine articulations shallowly incising the vertical striation of the outer surface.

Inner side with well-defined, bone-shaped main ridge well in agreement with that of holotype; no second ridge on inner side of ventral portion of LAP discernible; inner side of tentacle notch with coarsely meshed, horizontally stretched stereom, nearly as wide as half of the total ventral LAP edge width. Single large perforation bordering ventral tip of main ridge; no second, elongate perforation. Ventrodistal edge of ventral LAP portion with poorly defined, slightly prominent knob.

Remarks

These LAPs display the highly distinctive characters of the LAPs of extant species of Ophiotoma , in particular the very large tentacle notches, the spine articulations in shallow depressions or notches of the non-bulging, non-elevated distal edge, the large and strongly protruding ventral portion, and the widened dorsal tip of the ridge on the inner side. The LAPs in question thus seem best accommodated in Ophiotoma , acknowledging, however, that the discovery of articulated specimens might reveal substantial differences in general skeleton morphology warranting separation at the generic level. The shape of the large, ventral portion of the LAPs, the large perforation and the distinctly bone-shaped ridge on the inner side, and the development and spatial extent of the vertical striation on the outer surface unmistakably characterise the above-described LAPs, which is why they are here described as a new species of Ophiotoma .

Occurrence

Early Kimmeridgian of France.

Figures

Fig. 12. Lateral armplates (LAPs) of fossil and Recent ophiacanthidbrittle stars in external (a) and internal (b) views. 1. Ophiotoma assimilis Koehler, 1904, Recent, proximal LAP. 2-3. Ophiotoma megatreta (H.L. Clark, 1911), Recent. 2. Proximal LAP. 3. Median LAP. 4. Ophiotoma sp. nov. innom. from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria; NHMW 2012/0137/0009, median LAP. 5-7. Ophiotoma vadosa sp. nov. from the early Pliensbachian (Early Jurassic) of Blockley, Great Britain. 5. GZG.INV.78541 (holotype), proximal LAP. 6. GZG.INV.78542 (paratype), median LAP. 7. GZG.INV.78543 (paratype), distal LAP. 8-10. Ophiotoma charlottae sp. nov. from the early Kimmeridgian of the Pointe du Chay, France. 8. GZG.INV.78545 (holotype), proximal LAP. 9. GZG.INV.78546 (paratype), proximal to median LAP. 10. GZG.INV.78547 (paratype), distal LAP. One common scale bar per species is given.