Dermacantha leonorae, 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 : 165-166

Dermacantha leonorae sp. nov.

urn:lsid:zoobank.org:act:95EF2CA2-C31C-415F-A639-417842B0EEC6

Fig. 29 : 9-11

Diagnosis

Species of Dermacantha gen. nov. with small LAPs; proximal to median ones devoid of vertical striation on outer surface; five small spine articulations; single moderately well-defined spur near outer ventroproximal and inner ventro-distal tips of LAP; ridge on inner side very narrow but with strongly widened dorsal tip.

Etymology

Species named in hoinour of my friend and colleague Leonora Martín-Medrano, for her extraordinary hospitality and as an encouragement to her to pursue research in ophiuroid palaeontology.

Type material

Holotype GZG.INV.78710 .

Paratypes

GZG.INV.78711 and GZG.INV.78712.

Type locality and horizon

Blockley, near Cheltenham, Great Britain; shell lenses in clay matrix, Davoei Zone, early Pliensbachian, Early Jurassic.

Additional material

GZG.INV.78713 (7 dissociated LAPs).

Description

Holotype

GZG.INV.78710 is a dissociated, small, proximal LAP; slightly higher than wide; dorsal edge gently convex; distal edge convex; proximal edge concave, with single, moderately well-defined, prominent, horizontally elongate spur close to ventro-proximal tip of LAP; ventral sixth of LAP protruding ventroproximalwards; outer surface with very finely meshed stereom; no vertical striation; narrow band of very finely horizontally striated stereom along proximal edge. Five small, ear-shaped spine articulations in notches of non-elevated distal edge; dorsal and ventral lobes separated by small, thin knob; spine articulations proximally directly encompassed by outer surface stereom; spine articulations nearly of equal size; dorsalward increase in size of gaps separating spine articulations; gap between spine articulations and distal edge of LAP very narrow. Ventral edge of LAP with moderately large, very gently concave tentacle notch.

Inner side of LAP with moderately large, conspicuous, sharply defined, prominent, very narrow ridge; dorsal tip strongly enlarged, nearly triangular; ventral part of ridge pointing ventro-proximalwards, not merged with slightly thickened ventral portion of LAP, separated from dorsal part of ridge by gentle, rounded kink; well-defined, oval, slightly prominent knob on ventro-distal tip of LAP; inner side of tentacle notch relatively large, with coarsely meshed, horizontally elongate stereom, well defined laterally. Very short and narrow, rather deep and well-defined furrow dorsally bordering tentacle notch.

Paratype supplements and variation

GZG.INV.78711 is a dissociated median LAP; slightly wider than high; very well in agreement with holotype; dorsal edge very slightly concave; spur near ventro-proximal tip of LAP sharply defined, lenticular, strongly prominent, composed of more densely meshed stereom. Five spine articulations similar to those observed on holotype; dorsalward increase in size of gaps separating spine articulations slightly weaker; ventral and dorsal lobes of spine articulations separated by one to three very small knobs.

Inner side of LAP well in agreement with that of holotype; dorsal tip of ridge slightly less strongly widened. No furrow discernible.

GZG.INV.78712 is a dissociated distal LAP; slightly wider than high; ventro-distal tip of LAP strongly protruding ventralwards, rounded; trabeculae of outer surface stereom merging into short, poorly developed, irregular vertical striation close to spine articulations. Four spine articulations similar to those observed on holotype; dorsalmost spine articulation smallest; gap between spine articulations and distal edge of LAP moderately large, widening ventralwards. Ventral edge of LAP with large, deeply concave tentacle notch.

Inner side of LAP in agreement with that of holotype; dorsal tip of ridge slightly less strongly widened; spur on inner side of ventro-distal tip of LAP oblique. No furrow discernible.

Remarks

These LAPs are unambiguously assignable to Dermacantha gen. nov. on account of their spine articulation structure combined with the general Dermocoma -like morphology. They represent the sole LAP type within this genus which completely lacks a vertical striation on the outer surface. Closest similarities are shared with the LAPs of Dermacantha pattyana sp. nov., in particular those with reduced vertical striation on the outer surface. In the latter species, however, the ridge on the inner side is shorter and broader.

Occurrence

Early Pliensbachian of Great Britain.

Figures

Fig. 29. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1. Dermocoma sp. nov. innom. 4 from the early Albian (Early Cretaceous) of Leighton Buzzard, Great Britain; NHM EE 14844, proximal LAP. 2-5. Dermacantha pattyana gen. et sp. nov. from the Hettangian (Early Jurassic) of Fontenoille, Belgium. 2. MnhnL HE414 (holotype), proximal LAP. 3. MnhnL HE415 (paratype), proximal LAP. 4. MnhnL HE416 (paratype), median LAP. 5. MnhnL HE417 (paratype), distal LAP. 6-8. Dermacantha seeweni (Kutscher & Hary, 1991) comb. nov. from the late Sinemurian (Early Jurassic) of Bishop’s Cleeve, Great Britain. 6. GZG.INV.78706, proximal LAP. 7. GZG.INV.78707, median LAP. 8. GZG.INV.78708, distal LAP. 9-11. Dermacantha leonorae gen. et sp. nov. from the early Pliensbachian (Early Jurassic) of Blockley, Great Britain. 9. GZG.INV.78710 (holotype), proximal LAP. 10. GZG.INV.78711 (paratype), median LAP. 11. GZG.INV.78712 (paratype), distal LAP. One common scale bar per species.