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 : 120-121

Genus Hanshessia Thuy & Meyer, 2013

Type species

Hanshessia trochitophila Thuy & Meyer, 2013 , by original designation.

Diagnosis

Ophiacanthid with relatively large LAPs, proximal ones generally at least twice higher than wide; dorsal edge of proximal LAPs round, tongue shaped; ventral part of LAPs protruding ventro-proximalwards; numerous very large, ear-shaped spine articulations on strongly elevated distal portion of LAP; ridge on inner side composed of strongly bent ventral part and straight, near-vertical dorsal part closely paralleling proximal edge of LAP; tip of dorsal ridge part widely separated from dorsal edge of LAP; kink between dorsal and ventral parts of ridge devoid of ventro-proximalwards protruding angle.

Remarks

Hanshessia is an extinct genus described on the basis of articulated specimens from the Bajocian of Switzerland ( Thuy & Meyer 2013) and thus one of the very few fossil ophiacanthid genera for which detailed data on general skeletal morphology are available. The LAPs of the type specimens are well preserved and well known, at least as far as external structures are concerned. The morphology of the inner side, in contrast, could not be directly assessed on the basis of the type specimens. Upon careful re-examination of the latter, however, a few dissociated vertebrae exposing the vertical groove on the lateral side could be observed, allowing for conclusions on the shape of the ridge on the inner side of the LAPs. In fact, the lateral groove on the vertebrae and the ridge on the inner side of the LAPs serve as articulation interface between both skeletal components thus sharing complementary morphologies.

Judging from observations on the type specimens, the ridge on the inner side of Hanshessia trochitophila is composed of an oblique, strongly bent ventral part and a slightly longer, straight, near-vertical part sharply interrupted well below the dorsal edge of the LAP and separated from the ventral part by an angular, but not ventro-proximalwards extended, kink. In combination with the numerous, very large spine articulations, the tongue-shaped dorsal edge of the LAPs, and the ventro-proximally protruding ventral portion of the LAPs, the above-described ridge shape is highly distinctive. Closest similarities in LAP morphology are shared with the Ophiotreta - Ophiopristis group. In the latter, however, the ridge on the inner side, although superficially almost identical, generally displays a straight ventral part, a kink with a conspicuous ventro-proximally pointing angle, and a dorsal part which almost reaches the dorsal edge of the LAP. In addition, the LAPs of species of Ophiotreta and Ophiopristis are characterised by a strongly prominent, conspicuous distalmost lamella proximally bordering the spine articulations and commonly displaying a connecting ridge with the ventral lobe of the latter.