Ophiojagtus alternatus ( Kutscher & Jagt, 2000 ) 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 : 221-222

Ophiojagtus alternatus ( Kutscher & Jagt, 2000) comb. nov. Fig. 38 : 9-10

Ophiosmilax? alternatus Kutscher & Jagt, 2000 in Jagt 2000: 7 , pl. 1 figs 1-2.

Ophiosmilax? alternatus Kutscher & Jagt, 2000: 47-48 , pl. 31 figs 8-12, pl. 33 figs 9-11.

Ophiosmilax ? n. sp. – Jagt 1999a: 199, pl. 1 figs 1-2.

Ophiosmilax? alternatus – Jagt & Riegraf 2003: table 1.

non Ophiosmilax? alternatus – Štorc 2004: 397, figs 6-8. — Štorc & Žítt 2008: 124, fig. 4A-F.

Diagnosis

Species of Ophiojagtus gen. nov. with moderately large LAPs displaying an extremely long ventral portion, three to four spine articulations and an evenly bent, slender ridge on the inner side extending well onto the ventral portion.

Material examined

34 dissociated LAPs in the Manfred Kutscher Collection in Sassnitz, Germany, from the early Maastrichtian of Rügen, Germany, the type material of Kutscher & Jagt (2000); NHMM 2012 060, NHMM 2012 061 and NHMM JJ 3679 (13 dissociated LAPs) from the early late Maastrichtian of Haccourt, Belgium, the original material of Jagt (2000); GZG.INV.78819 (2 dissociated LAPs) from the late Campanian of Lägerdorf-Alsen, Germany.

Description

Moderately large, dissociated LAPs of stout, massive and strongly curved aspect; proximal ones more than twice higher than wide, distal ones less than 1.5 times higher than wide; dorsal edge weakly concave as a result of the pointed dorso-proximal tip of the LAP slightly protruding towards arm midline; distal edge convex; dorsal part of proximal edge evenly convex, ventral part concave; ventral portion of LAP narrow, extremely long, accounting for more than half of the total LAP height in proximal LAPs to slightly less than half of the total LAP height in distal ones; outer surface with finely meshed stereom. Three to four large, ear-shaped spine articulations freestanding on strongly bulging distal portion of LAP and composed of thick, continuous volute; dorsalward increase in size of spine articulations and of gaps separating them; gap between spine articulations and distal edge of LAP narrow.

Inner side of LAP with well-defined, prominent, slender, evenly bent ridge with ventral part extending well onto the ventral portion of the LAP, and widened dorsal tip with ventro-proximalwards pointing extension; no spurs on inner side of distal edge of LAP; inner side of tentacle notch very weakly defined, almost indiscernible. Small, irregular perforations in very shallow, poorly defined vertical furrow distally bordering ridge.

Remarks

Kutscher & Jagt (2000) first described this species on the basis of dissociated LAPs and vertebrae from the early Maastrichtian of Germany and Denmark. As noted above, the original assignment to the ophiomyxid Ophiosmilax , even if tentative, is untenable. The LAPs in question clearly belong to the new ophiacanthid genus Ophiojagtus gen. nov. Within this genus, they are unique in displaying three to four spine articulations, an extremely long ventral portion and a slender, evenly bent ridge on the inner side extending well onto the ventral portion of the LAP.

The LAPs described and illustrated as Ophiosmilax ? alternatus by Štorc (2004) from the Turonian of the Czech Republic and Tunisia display much more coarsely meshed stereom on the outer surface and thus most probably belong to a different, still unnamed species of the present genus. The LAPs described by Štorc & Žítt (2008) from the Turonian of the Czech Republic seem to display four to five, rather than three to four, spine articulations, which would challenge assignment to Ophiojagtus alternatus comb. nov. In order to clarify the exact systematic position of these Turonian occurrences of Ophiojagtus gen. nov., the original material needs to be re-examined, in particular the diagnostically important, but insufficiently described and unillustrated inner side.

Occurrence

Late Campanian of Germany, early Maastrichtian of Germany and Belgium.

Figures

Fig. 38. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-4. Ophiojagtus irimurai gen. et sp. nov. from the early Kimmeridgian (Late Jurassic) of the Pointe du Chay, France. 1. GZG.INV.78808 (holotype), proximal LAP. 2. GZG.INV.78809 (paratype), median LAP. 3. GZG.INV.78810 (paratype), median LAP. 4. GZG.INV.78811 (paratype), distal LAP. 5-7. Ophiojagtus acklesi gen. et sp. nov. from the late Aptian (Early Cretaceous) of Wizard Way, Texas. 5. GZG.INV.78814 (holotype), proximal LAP. 6. GZG.INV.78815 (paratype), median to distal LAP. 7. GZG.INV.78816 (paratype), proximal LAP. 8. Ophiojagtus sp. 1 from the early Cenomanian (Late Cretaceous) of Waco, Texas; proximal LAP. 9-10. Ophiojagtus alternatus (Kutscher & Jagt, 2000) comb. nov. from the early late Maastrichtian (Late Cretaceous) of Haccourt, Belgium. 9. NHMM 2012 060, proximal to median LAP. 10. NHMM 2012 061, proximal LAP. One common scale bar per species.