Ophiotoma, Verrill, 1899

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 : 57

Ophiotoma sp. nov. innom.

Fig. 12 : 4

Material examined

NHMW 2012/0137/0009 (dissociated LAP) from the late Sinemurian to early Pliensbachian of the Glasenbach Gorge, Austria.

Description

NHMW 2012/0137/0009 is a dissociated, small, proximal to median LAP, slightly wider than high; dorsal edge nearly straight; distal edge oblique, nearly straight to slightly convex; proximal edge strongly concave, devoid of spurs; ventral third of LAP strongly protruding ventro-proximalwards; distal portion of LAP not bulging and not elevated; outer surface almost entirely covered by fine, regular, vertical striation composed of thin distally slightly overlapping lamellae. Four ear-shaped, equi-distant spine articulations in tight, shallow notches of the the distal edge only very slightly interrupting the vertical striation; ventralmost spine articulation slightly smaller than remaining three; moderately large and ventrally increasing gap between spine articulations and distal edge of LAP; dorsal and ventral lobes of spine articulations forming continuous volute. Ventral edge of LAP with very large, concave tentacle notch.

Inner side of LAP: ridge very narrow, well defined, prominent, evenly bent, with widened dorsal tip reaching dorso-proximal corner of LAP; ventral tip pointing ventro-proximalwards, merging with ventral portion of LAP; no spurs discernible on inner side of distal edge of LAP; inner side of tentacle notch slightly wider than one-third of the ventral edge width of the LAP. Presence of perforations on the inner side not determinable on account of insufficient preservation.

Remarks

The single known LAP is characterised by the very large tentacle notch, the absence of a constriction or strongly elevated distal portion, and the spine articulations in shallow notches and devoid of connecting ridges with the outer surface ornament. This combination of characters strongly suggests assignment to Ophiotoma or at least to the fossil LAP types placed in Ophiotoma for the reasons discussed above. The LAP in question shows closest similarities to those of Ophiotoma charlottae sp. nov. (see below), but differs in having its outer surface almost entirely covered by vertical striation. In Ophiotoma vadosa sp. nov. the spine articulations show a strong dorsalward increase in size and in the gaps separating them. The LAP from the Glasenbach Gorge belongs to an undescribed species, but in view of the fact that a single specimen is available, any formal description is premature.

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.