Ophiacantha, Muller & Troschel, 1842

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 : 102

Ophiacantha sp. nov. innom 2

Fig. 18 : 10

Material examined

GZG.INV.78601 from the latest Aptian to earliest Albian of Blake Nose, tropical northeast Atlantic.

Description

GZG.INV.78601 is a dissociated, moderately large, distal LAP; more than twice wider than high; fragile; dorsal edge strongly concave as a result of a well-developed constriction; distal edge convex; proximal edge irregularly undulose, with large, very poorly defined, weakly prominent but strongly protruding spur in dorsal half; outer surface entirely covered with coarsely meshed stereom, slightly becoming finer close to proximal edge of LAP. Four large, equal-sized, equi-distant, near-circular spine articulations freestanding on strongly elevated distal portion of LAP; dorsal and ventral lobes of spine articulations thin, merged into continuous, near-circular volute; spine articulations proximally sharply bordered by vertical, straight, well-defined and prominent ridge; gap between spine articulations and distal edge of LAP relatively narrow, barely as wide as half a spine articulation. Ventral edge of LAP weakly concave, tentacle notch invisible in external view.

Inner side of LAP with large, moderately well-defined, prominent, straight, near-horizontal ridge; dorsal tip of ridge strongly widened, dorsally pointed, with ventro-proximally pointing extension; inner side of distal edge with moderately large, poorly defined, non-prominent spur composed of slightly more densely meshed stereom; inner side of tentacle notch relatively large. No perforations discernible.

Remarks

Only a single specimen of this LAP type is currently known. Although it is from distal arm portions, it displays characters strongly pointing to the genus Ophiacantha , in particular with regard to the shape of the ridge on the inner side, as well as the shape and arrangement of the spine articulations. Closest similarities are shared with LAPs assigned to Ophiacantha from the Albian of England (see below). These differ, however, in displaying a strongly undulose, rather than straight, ridge proximally bordering the spine articulations. The present LAP most probably represents a new species of Ophiacantha but in the absence of more material it cannot be formally described.

Figures

Fig. 18. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-2. Ophiotreta sp. nov. innom 2 from the Langhian (middle Miocene) of Stotzing (1) and Mannersdorf (2), Austria. 1. NHMW 2012/0139/0003, proximal LAP. 2. NHMW 2012/0139/0001, proximal LAP. 3-4. Europacantha paciphila gen. et sp. nov. from the late Anisian (Middle Triassic) of Felsöörs, Hungary. 3. MHI 2090/1 (holotype), proximal to median LAP. 4. MHI 2091/1 (paratype), proximal LAP. 5-7. Ophiacantha jaegeri sp. nov. from the latest Hauterivian (Early Cretaceous) of Sarstedt, Germany. 5. GZG.INV.78595 (holotype), proximal LAP. 6. GZG.INV.78596 (paratype), median LAP. 7. GZG. INV.78597 (paratype), distal LAP. 8-9. Ophiacantha sp. nov. innom 1 from the latest Aptian to earliest Albian (Early Cretaceous) of Blake Nose, NE Atlantic. 8. GZG.INV.78599, proximal LAP. 9. GZG. INV.78600, distal LAP. 10. Ophiacantha sp. nov. innom 2 from the latest Aptian to earliest Albian (Early Cretaceous) of Blake Nose, NE Atlantic; GZG.INV.78601, distal LAP. One common scale bar per species.