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 : 122

Hanshessia sp. nov. innom. 2

Fig. 21 : 7-9

Material examined

GZG.INV.78637, GZG.INV.78638, GZG.INV.78639 and GZG.INV.78640 (2 dissociated LAPs) from the lower Bathonian Zigzag Zone of La Pouza, France.

Description

GZG.INV.78637 is a dissociated, moderately large, proximal LAP; dorsal edge fragmentary; LAP originally more than twice higher than wide; ventral portion of LAP protruding ventro-proximalwards; distal edge convex; proximal edge irregularly undulose, with large, poorly defined, prominent and very strongly protruding spur; outer surface with well-developed, fine, slightly undulose vertical striation near spine articulations, composed by fine lamellae and replaced by finely meshed stereom on the proximal half of the outer surface. At least six very large, ear-shaped spine articulations in shallow notches on the strongly elevated distal portion of the 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 very poorly defined, weakly prominent, strongly undulose ridge; narrow gap between spine articulations and distal edge of LAP; weak dorsalward increase in size of spine articulations and gaps separating them. Ventral edge convex, with small, concave tentacle notch. Inner side of LAP with large, conspicuous, sharply defined, prominent ridge composed of strongly bent ventral part not merged with thickened ventral portion of LAP, and straight, near-vertical dorsal part closely paralleling proximal edge of LAP and abruptly interrupted well below dorsal edge of LAP; dorsal and ventral parts of ridge separated by angular kink devoid of conspicuous ventro-proximally protruding angle; inner side of distal edge of LAP with large, very weakly defined, almost indiscernible depression; inner side of tentacle notch small, moderately well defined laterally. Narrow, poorly defined, shallow vertical furrow with minute irragularly spaced perforations dorsally bordering tentacle notch.

GZG.INV.78638 is a dissociated, moderately large, proximal LAP fragment; ventral half missing; dorsal edge completely preserved, convex, tongue shaped; preserved portion of proximal edge devoid of spur; outer surface almost entirely with finely meshed stereom, only few weakly developed vertical lamellae between notches of spine articulations. Four very large spine articulations preserved, similar to those observed on above-described specimen; dorsalmost spine articulation slightly smaller than remaining three.

Inner side of LAP with narrow, sharply defined, prominent dorsal part of ridge abruptly interrupted well below dorsal edge of LAP. Well-defined, moderately wide and deep vertical furrow halfway between dorsal part of ridge and distal edge of LAP.

GZG.INV.78639 is a dissociated, small, distal LAP; ventral portion of LAP missing; LAP originally at least 1.5 times higher than wide; dorsal edge slightly convex; proximal edge with large, moderately well-defined, prominent and strongly protruding spur; outer surface almost entirely with finely meshed stereom in dorsal half of preserved LAP portion, and with narrow area of well-defined, fine vertical striation. Three spine articulations similar to those of above-described specimens preserved.

Inner side of LAP with large ridge similar to that of above-described specimen but with half of ventral part missing; inner side of distal edge of LAP with moderately large, very poorly defined, almost indiscernible depression. No perforations or furrows discernible.

Remarks

The shape of the ridge on the inner side, the structure and arrangement of the spine articulations and the outline of the dorsal tip of the LAPs unambiguously place the present material in the genus Hanshessia . In contrast to the LAPs of the nearly coeval type species, H. trochitophila , however, these LAPs display a well-developed vertical striation on their outer surface. The large, conspicuously protruding spur on the proximal edge of the LAPs clearly differentiates them from the ones (unnamed) from the Pliensbachian of Austria assigned to the same genus. The material described above represents a new species but in the absence of more complete specimens it cannot be described formally.

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.