Hanshessia, Thuy & Meyer, 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 : 121

Hanshessia sp. nov. innom. 1

Fig. 21 : 5-6

Material examined

NHMW 2012/0137/0021, NHMW 2012/0137/0022 and NHMW 2012/0137/0023 (4 dissociated LAPs) from the late Sinemurian to early Pliensbachian of the Glasenbach Gorge, Austria.

Description

Very large, dissociated proximal LAPs, with ventral portion missing; originally more than twice higher than wide; dorsal edge convex, tongue shaped; distal edge convex; preserved portion of poximal edge nearly straight to slightly concave, devoid of spurs; outer surface with fine, well-developed, slightly undulose, vertical striation confined to a narrow band close to spine articulations and composed of fine lamellae, replaced on most of outer surface by finely meshed stereom. At least four very large, earshaped spine articulations in shallow notches on strongly elevated distal portion of LAP; notches of spine articulations deeply incising vertical striation; ventral and dorsal lobes of spine articulations merged into continuous, near-circular volute; spine articulations proximally bordered by moderately well-defined, weakly prominent, strongly undulose ridge; dorsalward increase in size of spine articulations and of gaps separating them, but dorsalmost spine articulation smaller than second dorsalmost; gap between spine articulations and distal edge of LAP relatively narrow.

Inner side of LAPs with conspicuous, sharply defined, prominent, very narrow dorsal part of ridge, paralleling proximal edge of LAP, not reaching dorsal edge of LAP but abruptly interrupted well below the latter; angular kink at ventral tip of dorsal part of ridge, devoid of ventro-proximally pointing angle; ventral part of ridge not preserved; inner side of distal edge of LAP devoid of spurs; tentacle notch not preserved. Well-defined, narrow, vertical furrow with scattered, very small perforations.

Remarks

Despite its fragmentary nature, the above-described material is unambiguously assignable to Hanshessia on account of the shape of the ridge, the shape and arrangement of the spine articulations and the shape of the dorsal LAP edge. The present specimens differ from the other types of LAPs assigned to Hanshessia in displaying a fine vertical striation and lacking spurs on the outer proximal and inner distal edges. Unfortunately, the incompleteness of the material available precludes a formal description.

Figures

Fig. 21. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views and articulated arm fragment in ventral (a) and dorsal (b) views. 1. Ophiogaleus constrictus (Hess, 1966) comb. nov. from the late Oxfordian (Late Jurassic) of Savigna, France; GZG.INV.78627 distal arm fragment. 2. Ophiogaleus sp. from the early Kimmeridgian (Late Jurassic) of Geisingen, Germany; GZG.INV.78632, proximal LAP. 3-4. Ophiogaleus danicus (Rasmussen, 1952) comb. nov. from the early Maastrichtian (Late Cretaceous) of Rügen, Germany. 3. GZG.INV.78635, proximal LAP. 4. GZG. INV.78636, distal LAP. 5-6. Hanshessia sp. nov. innom. 1 from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 5. NHMW 2012/0137/0021, proximal LAP. 6. NHMW 2012/0137/0022, proximal LAP. 7-9. Hanshessia sp. nov. innom. 2 from the early Bathonian (Middle Jurassic) of La Pouza, France. 7. GZG.INV.78637, proximal LAP. 8. GZG.INV.78638, proximal LAP. 9. GZG.INV.78639, distal to median LAP. One common scale bar per species except for 1.