Ophiotreta hedone, 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 : 92-94

Ophiotreta hedone sp. nov.

urn:lsid:zoobank.org:act:959BB836-3EA8-4855-B7AC-3FCCADA44A8E

Fig. 17 : 12-15

Diagnosis

Species of Ophiotreta with very small LAPs displaying well-developed vertical striation; ventral sixth to third of LAP protruding ventro-proximalwards; up to five large spine articulations with moderately well-developed connecting ridge between ventral lobes and distalmost lamella of outer surface striation.

Etymology

Species named after Hedone, Greek for pleasure, as a homage to French “savoir-vivre”.

Type material

Holotype GZG.INV.78590 .

Paratypes

GZG.INV.78591, GZG.INV.78592 and GZG.INV.78593.

Type locality and horizon

Grignon, France; base of level 2 of Merle (2008), Campanile giganteum beds, middle Lutetian, Middle Eocene.

Additional material

GZG.INV.78594 (118 dissociated LAPs).

Description

Holotype

GZG.INV.78590 is a dissociated, small, proximal LAP; almost twice higher than wide; dorsal edge slightly concave as a result of a weak constriction; distal edge weakly convex to straight; proximal edge irregularly undulose, devoid of spurs; ventro-proximal portion of LAP missing; outer surface with fine, well-developed vertical striation composed of fine, slightly overlapping lamellae restricted to narrow band close to spine articulations, replaced by finely meshed stereom in all other parts of the outer surface. Five, large, ear-shaped spine articulations freestanding on strongly elevated distal portion of LAP and proximally bordered by undulose distalmost lamella; dorsal lobe large, separated from much smaller ventral lobe by small, shallow notch; short, weakly developed connecting ridge between ventral lobe of spine articulations and distalmost lamella; second dorsalmost spine articulation slightly larger than remaining four; very weak dorsalward increase in size of gaps separating spine articulations. Ventral edge of LAP fragmentary; tentacle notch not visible in external view.

Inner side of LAP with large, conspicuous, sharply defined ridge composed of near-vertical, straight dorsal part very close to proximal edge of LAP, and straight, oblique and slightly wider ventral part with ventrally pointing ventral tip; dorsal and ventral parts almost of equal length, separated by angular kink with conspicuous ventro-proximally pointing angle; very small, weakly prominent, inconspicuous and hardly discernible knob on ventral portion of LAP, widely separated from ridge; inner side of distal edge of LAP devoid of spurs; inner side of tentacle notch moderately large. Vertical row of moderately large, irregularly spaced perforations in very shallow, poorly defined furrow dorsally bordering inner side of tentacle notch.

Paratype supplements and variation

GZG.INV.78591 is a dissociated proximal LAP; generally in close agreement with holotype but ventroproximal sixth better preserved, slightly protruding ventro-proximalwards; proximal edge slightly undulose, devoid of spurs.

Inner side of LAP with almost indiscernible, weakly prominent and slightly elongate knob close to ventro-distal edge of ventral LAP portion, in addition to ridge similar to that observed on holotype. Two large, irregular perforations distally bordering ventral tip of ridge, no furrow discernible.

GZG.INV.78592 is a dissociated median LAP; slightly higher than wide; ventral third protruding ventroproximalwards; outer surface mostly covered by well-developed vertical striation composed of rather broad lamellae, replaced by finely meshed stereom in narrow band near proximal edge of LAP. Four spine articulations similar to those observed in holotype. Ventral edge of LAP oblique, tentacle notch invisible in external view.

Inner side of LAP with oblique, straight ridge similar to the ventral part of the ridge observed in the holotype, and with a widened dorsal tip; large, prominent but poorly defined, elongate knob near ventrodistal edge of LAP. Two to three moderately large perforations loosely arranged in vertical row dorsally bordering inner side of tentacle notch; no furrow discernible.

GZG.INV.78593 is a dissociated distal LAP; slightly wider than high; ventral third to quarter of LAP slightly protruding ventro-proximalwards; well-developed striation on outer surface restricted to narrow band near spine articulations. Four spine articulations, two median ones larger than ventral and dorsal ones; ventral lobe of spine articulations slightly thickened into small knob, with short, thin, yet welldeveloped connecting ridge with distalmost lamella.

Inner side of LAP with oblique, straight ridge similar to the ventral part of the ridge observed in the holotype, and with a widened dorsal tip; no ventral knob discernible; inner side of tentacle notch relatively small. No perforations discernible.

Remarks

These LAPs are unambiguously assignable to the Ophiotreta - Ophiopristis group mainly on account of the highly distinctive shape of the ridge on the inner side. On the basis of the moderately well-developed connecting ridge between the ventral lobe of the spine articulations and the distalmost lamella of the outer surface striation, even in proximal LAPs, Ophiotreta is preferred here. Their very small size, low number of spine articulations and unusually long ventral portion make these LAPs incompatible with any other fossil LAP type assigned to Ophiotreta .

Occurrence

Middle Lutetian of France.

Figures

Fig. 17. Fossil skeletal plates of ophiacanthid brittle stars; lateral arm plates (LAPs) in external (a) and internal (b) views. 1-2. Ophiotreta striata (Kutscher & Jagt, 2000) comb. nov. from the early Maastrichtian of Rügen, Germany. 1. GZG.INV.78588, proximal LAP. 2. GZG.INV.78589, distal LAP. 3-11. Ophiotreta dendrophyllicola sp. nov. from the middle Danian (Paleocene) of Fakse, Denmark. 3. MGUH 30236 (holotype), proximal LAP. 4. NHMM 2012 050 (paratype), median LAP. 5. NHMM 2012 051 (paratype), distal LAP. 6. NHMM 2012 052 (paratype), vertebra in distal view. 7. NHMM 2012 053 (paratype), vertebra in proximal view. 8. NHMM 2012 054 (paratype), vertebra in dorsal view. 9. NHMM 2012 055 (paratype), oral plate in adradial (a) and abradial (b) view. 10. NHMM 2012 056 (paratype), arm spine fragment. 11. NHMM 2012 057 (paratype), arm spine fragment. 12-15. Ophiotreta hedone sp. nov. from the middle Lutetian (Eocene) of Grignon, France. 12. GZG.INV.78590 (holotype), proximal LAP. 13. GZG.INV.78591 (paratype), median LAP. 14. GZG.INV.78592 (paratype), distal LAP. 15. GZG.INV.78593 (paratype), median LAP. One common scale bar per species.