Reitneracantha, 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 : 203

Genus Reitneracantha gen. nov.

urn:lsid:zoobank.org:act:3BFFDD52-C9E7-450B-9001-E09134B80477

Type, and only known, species

Reitneracantha dissidens sp. nov.

Diagnosis

Ophiacanthid with moderately large LAPs devoid of conspicuous outer surface ornament or spurs on the outer proximal edge; up to five large to very large, ear-shaped spine articulations freestanding on the strongly elevated distal third or half of the LAP; proximal edge of the spine articulation irregularly corrugated; dorsal lobe of the spine articulations vertically elongate, much larger than ventral one; dorsalmost spine articulation invariably largest, conspicuously dorsalwards pointing, in proximal LAPs well below dorsal edge of LAP; ridge on inner side relatively short with widened dorsal tip; tentacle notch small, well defined laterally, semi circular.

Etymology

Genus named in honour of my friend and colleague Joachim Reitner, for his generous support and the delightfully shared delicacies and wines; from Acantha , a nymph in Greek mythology whose name literally translates to “thorny”; gender feminine.

Remarks

A very unusual type of dissociated LAPs was recovered from Early Jurassic deep-sea sediments of Austria. The presence of large, ear-shaped spine articulations with a sigmoidal fold, combined with the absence of a single large perforation on the inner side, clearly place these in the Ophacanthidae. Within this family, such LAPs are close to those of extant Ophiocamax . The most important similarities include the position of the spine articulations on the strongly elevated distal third or half of the LAP, the central notch in the dorsal lobe of the spine articulations, the strong dorsalward increase in size of the spine articulations, the conspicuously dorsalwards pointing dorsalmost spine articulation well below the dorsal edge of the LAP, the lack of a conspicuous outer surface ornament, the widened dorsal tip of the ridge on the inner side of the LAPs, and the very small, well-defined, semi-circular tentacle notch.

The shape of the spine articulations in these fossil LAPs, however, differs in displaying an irregularly corrugated proximal edge of the volute. In addition, the dorsal lobe of the spine articulations in the fossil LAPs is dorsally elongate and much larger than the ventral one. On account of these minor, yet significant, differences, the present LAPs are here assigned to a new genus, Reitneracantha gen. nov. However, similarities in LAP morphology are so close that Reitneracantha gen. nov. and Ophiocamax most probably share close phylogenetic ties. From an LAP morphological perspective, the phylogenetic relationships between Reitneracantha gen. nov. and Ophiocamax are probably even closer than between the latter and its extant sister taxon Ophiomitra . Thus, Reitneracantha gen. nov. and Ophiocamax are here considered to be members of the same lineage.