Dermocoma faberi, 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 : 140-143

Dermocoma faberi sp. nov.

urn:lsid:zoobank.org:act:563DC91F-6457-4DDE-A0EE-A4C9D2A04770

Fig. 26 : 1-3

Ophiacantha? toarcensis – Thuy 2005: 40, pl. 5 figs 1-6 (material incorrectly assigned to Ophiacantha? toarcensis Hess, 1962 ).

Diagnosis

Species of Dermocoma with large LAPs displaying a fine, vertical striation on almost entire outer surface; up to four spurs on outer proximal and inner distal edges; up to six relatively small spine articulations.

Etymology

Species named in honour of Alain Faber, who provided valuable support, especially at the very beginning of my palaeontological studies.

Type material

Holotype

MnhnL HE408 .

Paratypes

MnhnL HE409 and MnhnL HE410.

Type locality and horizon

Vance, Belgium; sample Van1 of Thuy (2005), Planorbis Zone , early Hettangian, Early Jurassic.

Additional material

MnhnL HE411 (385 dissociated LAPs), MnhnL HE256 and HE 257 (7 dissociated LAPs), original material from sample Van1 of Thuy (2005); MnhnL HE412 (239 dissociated LAPs), original material from sample Van2 of Thuy (2005); MnhnL HE413 (457 dissociated LAPs) from level c of Delsate et al. (2002), Liasicus Zone, Hettangian of Fontenoille, Belgium; original material of Thuy (2005) from the Hettangian of Bourglinster, Bereldange and Bridel in Luxembourg.

Description

Holotype

MnhnL HE408 is a dissociated, large, proximal LAP; approximately 1.5 times higher than wide, with oblique, slightly concave dorsal edge as a result of a very weak constriction; distal edge weakly convex; ventral quarter of LAP protruding ventro-proximalwards; proximal edge of LAP gently concave, with four horizontally elongate, prominent and strongly protruding, poorly defined but conspicuous spurs; second dorsalmost spur in the centre of the proximal edge, more than twice larger than remaining three spurs of near-equal size; outer surface with fine vertical striation consisting of thin, slightly distalwards overlapping lamellae; striation covering almost entire outer surface, with slight irregularities in ventral half of outer surface, otherwise very regularly vertical; lamellae decreasing in size and fading into finely meshed stereom towards proximal edge of LAP. Six relatively small, ear-shaped spine articulations in notches of distal edge interrupting vertical striation; no connecting ridge between spine articulation and striation; spine articulations of nearly equal size, with very weak dorsalward increase in size; dorsal and ventral lobes forming continuous, round lobe; very strong dorsalward increase in size of gaps separating spine articulations; relatively wide gap between spine articulations and distal edge of LAP. Ventral edge of LAP with moderately large, gently concave tentacle notch.

Inner side of LAP with narrow, sharply defined, prominent ridge separated by gentle kink into ventral and dorsal portions; dorsal portion oblique with dorsal tip widened, less sharply defined and bent dorsalwards; ventral portion bent proximalwards, slightly less prominent and more weakly defined than dorsal portion but not merged with thickened ventral edge of LAP; inner side of distal edge thin and with relatively wide vertical band of finely meshed stereom sharply separated from coarsely meshed stereom of remaining inner side; four relatively small, horizontally elongate, poorly defined, prominent, albeit not protruding, spurs in finely meshed band of distal edge; second dorsalmost spur slightly larger than remaining three. Tentacle notch relatively large, proximally bordered by thickened ventral edge of LAP, and distally by short nearly vertical ridge close to ventro-distal tip of LAP. Hardly discernible, irregular, vertical row of perforations at boundary between finely meshed stereom of distal edge and coarsely meshed stereom of remaining inner surface.

Paratype supplements and variation

MnhnL HE409 is a dissociated median LAP, slightly higher than wide; dorsal edge oblique, nearly straight to slightly convex; proximal edge slightly broken, with only single poorly defined, slightly prominent and protruding, horizontally elongate spur approximately in centre of proximal edge. Four ear-shaped, nearly equal-sized spine articulations; dorsalward increase in size of gaps separating spine articulations.

Inner side of LAP with ridge similar to that in holotype; inner side of distal edge with two weakly defined, slightly prominent, horizontally elongate ridges, ventral one of which slightly better defined and protruding as a result of the distal edge of the LAP being broken.

MnhnL HE410 is a dissociated distal LAP; twice wider than high, of nearly perfectly rectangular outline; dorsal and ventral edges straight; distal edge slightly convex, proximal straight, bordered by with oblique dorso-proximal and ventro-proximal tips of LAP; no spurs discernible on proximal edge. Three spine articulations sunken into notches of distal edge. Ventralmost spine articulation ventro-distally bordered by tentacle perforation.

Inner side of LAP with sharply defined, short, oblique ridge, slightly pointed dorso-proximally and ventro-distally; distal edge of LAP with two very weakly defined, slightly protruding spurs near dorso- and ventro-distal tips of LAP. Large tentacle perforation in the centre of the distal half of the LAP.

Remarks

These specimens were originally recorded by Thuy (2005) as Ophiacantha ? toarcensis Hess, 1962 , who acknowledged that they were not entirely compatible with the diagnosis of the species. The discrepancies in LAP morphology, originally interpreted as within-species variability ( Thuy 2005), are here identified as differences of systematic importance warranting separation at the specific level, in line with the observations by Thuy & Stöhr (2011) on variability patterns in LAP morpologies of extant ophiuroid species.

The size, shape and position of the spine articulations, the outer surface ornament and the shape of the ridge on the inner side strongly suggest that these LAPs are assignable to Dermocoma . Within this genus, greatest similarities are, indeed, shared with Dermocoma toarcensis comb. nov., originally described as Ophiacantha ? toarcensis , on account of the higher number of spine articulations and spurs on the outer proximal and inner distal edges. However, the present LAPs differ in displaying up to four, rather than three, spurs, as well as smaller spine articulations on a less strongly elevated distal portion of the LAP.

Occurrence

Hettangian of Belgium and Luxembourg.

Figures

Fig. 26. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-3. Dermocoma faberi sp. nov. from the Hettangian (Early Jurassic) of Vance, Belgium. 1. MnhnL HE408 (holotype), proximal LAP. 2. MnhnL HE409 (paratype), median LAP. 3. MnhnL HE410 (paratype), distal LAP. 4-6. Dermocoma potti sp. nov. from the late Pliensbachian (Early Jurassic) of Feuguerolles, France. 4. GZG.INV.78675 (holotype), proximal LAP. 5. GZG.INV.78676 (paratype), median LAP. 6. GZG. INV.78677 (paratype), distal LAP. 7-8. Dermocoma toarcensis (Hess, 1962) comb. nov. from the late Toarcian (Early Jurassic) of Seewen, Switzerland. 7. NHMB M11216, proximal LAP. 8. NHMB M11217, distal LAP. 9-11. Dermocoma longwyensis sp. nov. from the early Bajocian (Middle Jurassic) of Longwy, France. 9. GZG.INV.78679 (holotype), proximal LAP. 10. GZG.INV.78680 (paratype), median LAP. 11. GZG.INV.78681 (paratype), distal LAP. One common scale bar per species.