Ophioleviathan, 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 : 193-194

Genus Ophioleviathan gen. nov.

urn:lsid:zoobank.org:act:3AF8EB01-EA44-4C91-9614-CCFBE921662C

Type and sole known species

Ophioleviathan watsoni sp. nov.

Diagnosis

Ophiacanthid with extremely large, thick and massive LAPs; outer surface devoid of conspicuous ornament elements; no spurs on outer proximal and inner distal edges; poorly defined, slightly depressed narrow band along the middle part of the proximal ridge in proximal LAPs; up to seven large, ear-shaped spine articulations in deep notches of strongly bulging distal portion of LAP; spine articulations vertical to slightly overturned, with rather slender, rugged distal lobe merged with much larger, thicker and more strongly prominent distal lobe into continuous volute; inner side with extremely large, wide, slightly dorso-proximalwards bent, tongue-shaped ridge devoid of kinks and widest dorsally; tentacle notch very small and poorly defined.

Etymology

Name composed of ophis, Greek for “snake”, a commonly used prefix in ophiuroid names, and “Leviathan”, a biblical sea monster literally translating into “coiled, twisted”, referring to the genus as an unusually large ophiuroid with arms capable of considerable coiling that lived in the greater depths of the ancient Tethys Ocean; gender masculine.

Remarks

Lower Jurassic Tethyan deep-sea sediments from Austria have yielded one of the most extraordinary types of dissociated LAPs, characterised by an unusually large size, a very thick and massive aspect, and an exceptionally large ridge on the inner side. The presence of a sigmoidal fold in the spine articulations unambiguously places the LAPs in question in the family Ophiacanthidae , in spite of their highly unusual morphology. Within this family, greatest similarities are shared with the LAPs of the extinct ophiacanthid Inexpectacantha , especially on account of the massive and thick aspect, the lack of outer surface ornament and of spurs on the outer proximal and inner distal edges, the shape of the spine articulations and of the ridge on the inner side, and the very small, poorly defined tentacle notches. As a matter of fact, very similar LAPs from near-coeval, deeper-water sedimentary rocks of Switzerland, considered here to be conspecific with the LAP type in question, were described by Hess (2006) and assigned by him to Inexpectacantha lunaris comb. nov.

In spite of the striking similarities, the above-mentioned LAPs differ from those of Inexpectacantha in several aspects: they are considerably larger, thicker and display a larger height/width ratio, the spine articulations are vertical to slightly overturned and in deeper notches, the distal (dorsal) lobe of the spine articulations is much larger, thicker and more prominent than the proximal (ventral) lobe, the ridge on the inner side of the LAPs is much larger and wider, and the dorsal and ventral tips of the inner side protrude towards the arm midline. These differences are here considered to warrant separation at the generic level. Ophioleviathan gen. nov. is thus introduced here to accommodate the above-mentioned LAP type.

Ophioleviathan gen. nov. and Inexpectacantha are most probably sister taxa, as suggested by the highly distinctive spine articulation morphology and shape of the ridge on the inner side shared by both genera and not found in any other ophiacanthid. In terms of LAP morphology, Ophioleviathan gen. nov. is closer to the less paedomorphic group within Inexpectacantha , formed by I. ritae sp. nov. and I. lunaris comb. nov. (see above), especially on account of the larger size, the larger height/width ratio and the position of the spine articulations in notches. The LAPs of Ophioleviathan gen. nov., however, have an even less paedomorphic appearance than those of the above-mentioned group within Inexpectacantha .