Ophiacantha jaegeri, 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 : 99-101

Ophiacantha jaegeri sp. nov.

urn:lsid:zoobank.org:act:A991EFFE-BA53-46CC-B06A-84E27C84A749

Fig. 18 : 5-7

Diagnosis

Species of Ophiacantha with moderately large LAPs displaying a rather knobby general aspect; single poorly defined, protruding spur on outer proximal edge; outer surface devoid of vertical striation, with

coarsely meshed stereom displaying thickened trabecular intersections; up to six large spine articulations proximally bordered by knobby, undulose ridge; tentacle notch invisible in external view.

Etymology

Species named in honour of Manfred Jäger, who kindly provided the sample yielding the type material of the species.

Type material

Holotype GZG.INV.78595 .

Paratypes

GZG.INV.78596 and GZG.INV.78597.

Type locality and horizon

Claypit Gott in Sarstedt, Germany; latest Hauterivian, Early Cretaceous.

Additional material

GZG.INV.78598 (6 dissociated LAPs).

Description

Holotype

GZG.INV.78595 is a dissociated, moderately large LAP; approximately 1.5 times higher than wide; dorsal edge oblique, very weakly concave; distal edge evenly convex; proximal edge irregularly undulose, with small, poorly defined, weakly prominent but conspicuously protruding spur in its centre; outer surface with coarsely meshed stereom with trabeculae thickened into conspicuously large granules in ventral sixth of outer surface and into smaller granules in remaining outer surface; narrow band of finely meshed stereom along proximal edge. Six large, ear-shaped spine articulations freestanding on strongly elevated distal portion of LAP; ventral and dorsal lobes fused into near-round, continuous volute; spine articulations proximally bordered by knobby, wavy vertical ridge; dorsalward increase in size of spine articulations and in of gaps separating them; gap between spine articulations and distal edge of LAP as wide as one spine articulation. Ventral edge of LAP slightly convex, tentacle notch invisible in external view.

Inner side with large, conspicuous, sharply defined and prominent ridge composed of oblique, nearstraight main part with pointed dorsal tip and with ventro-proximally pointing dorsal extension slightly longer than main part and merged with the latter into near-triangular, vertically elongate knob; ventral portion of main ridge part with rounded kink and short ventro-proximally pointing extension; inner side of distal edge of LAP with small, poorly defined and hardly prominent spur composed of slightly more densely meshed stereom; inner side of tentacle notch relatively small, well defined laterally. Shallow but moderately well-defined vertical furrow dorsally bordering tentacle notch with small, irregularly spaced perforations.

Paratype supplements and variation

GZG.INV.78596 is a dissociated median LAP; nearly as high as wide; generally closely matching holotype; spur on proximal edge very weakly defined, almost indiscernible, not protruding. Five spine articulations similar to those observed on holotype; gap between spine articulations and distal edge of LAP narrower than one spine articulation. Ventral edge with very shallow, poorly developed tentacle notch.

Inner side of LAP with large, conspicuous, relatively wide, oblique ventralwards bent ridge with widened, nearly triangular dorsal tip; no spur discernible on inner side of distal LAP edge; inner side of tentacle notch relatively small, well defined laterally. Very shallow and weakly defined furrow dorsally bordering tentacle notch, no perforations clearly discernible.

GZG.INV.78597 is a dissociated distal LAP; almost twice wider than high; generally well in agreement with holotype but poorly preserved; dorsal edge strongly concave as a result of a well-developed constriction; no spur discernible on outer proximal edge; outer surface with coarsely meshed stereom replaced by finely meshed stereom in proximal third of outer surface; few trabecular intersections, especially in ventral part of outer surface, thickened into small granules. Four poorly preserved spine articulations on elevated distal portion of LAP, seemingly similar to those observed on holotype. Tentacle notch not visible in external view.

Inner side of LAP with large, moderately well-defined, oblique ridge with narrow, rounded dorsal tip and strongly widened ventral part; inner side of tentacle notch relatively small, moderately well defined laterally. Single, poorly defined perforation dorsally bordering tentacle notch, no furrow discernible.

Remarks

The shape of the ridge on the inner side in combination with the continuous, round volute of the spine articulations and the single spur on the outer proximal and inner distal edges strongly suggest that these LAPs to belong to the genus Ophiacantha or at least to a very closely related, yet undescribed genus. Morphological similarities are much closer to Ophiacantha than to the allegedly closely related Ophiogaleus gen. nov., which is why the LAPs in question are here assigned to the former genus. Among the fossil LAP types assigned to Ophiacantha , the ones described above are unique in lacking a vertical striation and at the same time in displaying a generally knobby appearance, with trabecular intersections thickened into small granules especially on the ventral portion of the outer surface but also in other parts, and with the conspicuously knobby ridge proximally bordering the spine articulations.

Occurrence

Latest Hauterivian of Germany.

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.