Ophiocamax Lyman, 1878

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 : 198-199

Genus Ophiocamax Lyman, 1878

Type species

Ophiocamax vitrea Lyman, 1878 , by monotypy.

Diagnosis

Ophiacanthid with large to very large LAPs commonly devoid of any conspicuous outer surface ornament; single variably well-defined, protruding spur on outer proximal and inner distal edges; large to very large ear-shaped spine articulations freestanding on strongly elevated distal third or even half of the proximal and median LAPs, with especially the dorsal spine articulations commonly widely separated from distal edge of LAP; elevated portion of LAP commonly beset with scattered thorns or granules; dorsalmost spine articulation at some distance from dorsal edge of LAP, commonly pointing dorsalwards; dorsalmost and second dorsal spine articulations often much smaller than remaining ones; dorsal lobe of spine articulations with conspicuous central notch; ridge on inner side with strongly widened, generally short, triangular dorsal tip and evenly ventro-proximally bent ventral part; tentacle notch very small, deeply incised, well defined and generally at least semi circular.

Remarks

Ophiocamax is one of the most distinctive and homogeneous genera in the Ophiacanthidae , consistently displaying a number of characters not found in any other ophiacanthid. The same holds true for the LAPs of Ophiocamax ( Fig. 35 : 1-6), at least for the species examined herein with respect to their LAP morphologies, namely O. austera Verrill, 1899 , O. fasciculata Lyman, 1883 , O. hystrix Lyman, 1878 and the type species, O. vitrea . In fact, the LAPs of Ophiocamax display several highly distinctive features, including spine articulations freestanding in the middle of the strongly elevated distal third or even half of the LAPs and thus commonly widely separated from the distal edge of the LAP, dorsalwards pointing dorsalmost spine articulations well below the dorsal edge of the LAP, dorsalmost and second dorsal spine articulations which are often much smaller than the remaining ones, and a very small, welldefined and at least semi-circular tentacle notch. In addition, the dorsal lobe of the spine articulations of Ophiocamax displays a conspicuous central notch, which results in spine articulations that are seemingly composed of proximal and distal rather than dorsal and ventral lobes.

The LAPs of extant Ophiomitra Lyman, 1869 ( Fig. 34 : 8-9), sister to Ophiocamax , share some important characters with the LAPs of the latter, in particular the spine articulations freestanding on the strongly elevated distal third or half of the LAP, the lack of a conspicuous outer surface ornament, and the strongly widened dorsal tip of the ridge on the inner side. In contrast to the LAP of Ophiocamax , however, those of Ophiomitra display nearly equal-sized spine articulations the dorsalmost of which commonly being very close to the dorsal edge of the LAP. In addition, the dorsal lobe of the spine articulation in Ophiomitra lacks the central notch.

Thanks to the numerous highly distinctive characters, the LAPs of Ophiocamax are expected to be easily recognised in the form of dissociated fossil LAPs. Yet, only very few occurrences of dissociated LAPs and articulated arm fragments assignable to Ophiocamax are currently known from shallowwater settings, and all are from the Oxfordian. Another record from deep-sea deposits is noticeably fundamentally similar to the LAPs of extant Ophiocamax but differs in a few minor respects and is thus assigned to a new, most probably very closely related, genus, Reitneracantha gen. nov. (see below).

Figures

Fig. 35. Skeletal plates and arm fragments of fossil and Recent ophiacanthid brittle stars; lateral arm plates (LAPs) in external (a) and internal (b) views. 1-3. Ophiocamax vitrea Lyman, 1878, Recent. 1. Proximal LAP. 2. Median LAP. 3. Dorsal arm plate. 4-5. Ophiocamax hystrix Lyman, 1878, Recent. 4. Proximal LAP. 5. Median LAP. 6. Ophiocamax austera Verrill, 1899, Recent; proximal LAP. 7-11. Ophiocamax dorotheae sp. nov. from the late Oxfordian (Late Jurassic) of Savigna, France. 7. GZG.INV.78763 (holotype), proximal LAP. 8. GZG.INV.78764 (paratype), median LAP. 9. GZG.INV.78765 (paratype), distal LAP. 10. GZG.INV.78766 (paratype), proximal arm fragment in ventral view. 11. GZG.INV.78767 (paratype), median arm fragment in dorsal view. One common scale bar per species except for 10 and 11.

Fig. 34. Lateral arm plates (LAPs) of fossil and Recent ophiacanthid brittle stars in external (a) and internal (b) views. 1-4. Ophioleviathan watsoni gen. et sp. nov. from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 1. NHMW 2012/0137/0024 (holotype), proximal LAP. 2. NHMW 2012/0137/0025 (paratype), proximal LAP. 3. NHMW 2012/0137/0026 (paratype), median LAP. 4. NHMW 2012/0137/0027 (paratype), distal LAP. 5-7. Manfredura curvata (Kutscher & Jagt, 2000) comb. nov. from the early Maastrichtian (Late Cretaceous) of Rügen, Germany. 5. GZG.INV.78759, proximal LAP. 6. GZG.INV.78760, median LAP. 7. GZG.INV.78761, distal LAP. 8-9. Ophiomitra valida Lyman, 1869, Recent. 8. Proximal LAP. 9. Median LAP. One common scale bar per species.