Ophiochondrus Lyman, 1869

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 : 208-209

Genus Ophiochondrus Lyman, 1869

Type species

Ophiochondrus convolutus Lyman, 1869 , by monotypy.

Diagnosis

Ophiacanthid with small LAPs of massive, thick and rounded aspect; outer surface commonly with thickened trabeculae in some cases merged into a poorly developed vertical striation; generally a single, variably well-defined, protruding spur in the middle of the proximal edge, ventrally bordered by a slightly depressed area of finely meshed stereom; small, oval, horizontally slightly elongate spine articulations freestanding and evenly distributed on very weakly elevated distal portion of the LAP; dorsal and ventral lobes of spine articulations separated proximally; spine articulations of equal size or with weak dorsalward decrease in size; ridge on inner side of LAPs moderately well defined, short, with ventro-proximalwards projecting extension of dorsal tip; tentacle notch very small, poorly defined, almost inconspicuous.

Remarks

Ophiochondrus has traditionally been considered to be a member of the Hemieuryalidae Verrill, 1899 (e.g., Matsumoto 1917; Fell 1960; Smith et al. 1995), although the ophiacanthid affinities of the genus have repeatedly been hinted at ( Mortensen 1927, 1936; O’Hara & Stöhr 2006). Eventually, Martynov (2010) transferred Ophiochondrus to the Ophiacanthidae , along with the other former hemieuryalid Ophiomoeris Koehler, 1904 , on the basis of spine articulation morphology. This transfer is corroborated by the phylogenetic anaylsis of Thuy et al. (2012) and the revised phylogeny presented herein.

Indeed, in terms of LAP morphology ( Fig. 37 : 1-3), Ophiochondrus is closely similar to the ophiacanthid genera Ophiolamina Stöhr & Segonzac, 2006 , Ophiohamus O’Hara & Stöhr, 2006 and, to a lesser extent, Ophiolebes . The LAPs of Ophiochondrus can be easily differentiated from those of Ophiohamus and Ophiolamina on the basis of the shape and position of the spine articulations. Unfortunately, knowledge of the LAP morphology of Ophiomoeris is incomplete, in particular with respect to the structures on the inner side, which hampers the elaboration of a comprehensive diagnosis of LAP morphology for Ophiochondrus . However, since the LAPs of the type species of Ophiochondrus are well known, an attempt is made here to work out a diagnosis of LAP morphology for the genus. This is all the more important because the ophiacanthid fossil record includes a type of dissociated LAPs which has a lot in common with the LAPs of extant Ophiochondrus .

Figures

Fig. 37. Lateral arm plates (LAPs) of fossil and Recent ophiacanthid brittle stars in external (a) and internal (b) views. 1-2. Ophiochondrus convolutus Lyman, 1869, Recent. 1. Proximal LAP. 2. Median LAP. 3. Ophiochondrus stelliger Lyman, 1879, Recent; proximal LAP. 4-5. Ophiochondrus punctatus (Kutscher & Jagt, 2000) comb. nov. from the early Maastrichtian (Early Cretaceous) of Rügen, Germany. 4. GZG.INV.78775, proximal LAP. 5. GZG.INV.78776, distal LAP. 6-7. Ophiochondrus? semirotundus (Kutscher & Jagt, 2000) comb. nov. from the early Maastrichtian of Rügen, Germany. 6. GZG.INV.78800, proximal LAP. 7. GZG.INV.78801, median LAP. 8-9. Ophiacanthidae gen. et sp. nov. innom. from the late Oxfordian (Late Jurassic) of the Plettenberg, Germany. 8. GZG.INV.78802, proximal LAP. 9. GZG.INV.78803, median or distal LAP. 10-11. Ophiojagtus argoviensis (Hess, 1966) comb. nov. from the late Oxfordian (Late Jurassic) of Savigna, France. 10. NHMB M1124, proximal LAP. 11. NHMB M11225, proximal to median LAP. One common scale bar per species.