Dermacantha carli, 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 : 169-170

Dermacantha carli sp. nov.

urn:lsid:zoobank.org:act:3FDC618A-F737-47FC-B0BA-9AE3CD84B586

Fig. 30 : 4-6

Diagnosis

Species of Dermacantha gen. nov. with moderately large LAPs generally displaying a vert small height/ width ratio, with even proximal LAPs slightly wider than high; two small, nearly equal-sized, welldefined, proximally pointed, prominent spurs on outer proximal edge; distal quarter of outer surface with regular, well-defined vertical striation; four relatively small spine articulations with dorsal and ventral lobes separated by small knob; three dorsal spine articulations in distal LAPs with conspicuous lip-shaped distal knob; ridge on inner side small very slender, with very weakly widened, strongly oblique dorsal part.

Etymology

Species named in honour of Carl, my friend, companion, family member, for his cheerful support and all the ideas that emerged during the many outdoor walks with him.

Type material

Holotype GZG.INV.78718.

Paratypes

GZG.INV.78719 and GZG.INV.78720.

Type locality and horizon

Plettenberg near Balingen, Germany; clay pockets between sponge associations in the lowest bed exposed in the quarry, Bimammatum Zone, late Oxfordian, Late Jurassic.

Additional material

GZG.INV.78721 (300 dissociated LAPs) from the late Oxfordian of the Plettenberg, Germany; GZG. INV.78722 (64 dissociated LAPs) from the Lacunosa Marls, early Kimmeridgian of Geisingen, Germany.

Description

Holotype

GZG.INV.78718 is a dissociated, moderately large, proximal LAP; slightly wider than high; dorsal edge slightly concave as a result of a weakly developed constriction; distal edge convex; proximal edge concave, with two small, well-defined, prominent, slightly protruding, proximally pointed spurs composed of densely meshed stereom; dorsal spur slightly larger than ventral one; ventral quarter of LAP strongly protruding ventro-proximalwards; ventro-distal tip of LAP protruding ventralwards, rounded; outer surface with narrow band of regular, vertical striation composed of rather broad, overlapping lamellae close to spine articulations, replaced by finely meshed stereom on proximal three-quarters of outer surface. Four relatively small, ear-shaped spine articulations in shallow notches of slightly elevated distal portion of LAP; ventral lobe of spine articulation separated from dorsal one proximally by small knob, and connected with distalwards projecting tip of outer surface stereom separating notches; spine articulations proximally separated by edge of notches; dorsalward increase in size of gaps separating spine articulations; ventralmost spine articulation slightly smaller than remaining, nearly equal-sized ones; notches very shallowly incising vertical striation; gap between spine articulations and distal edge of LAP almost as wide as one spine articulation. Ventral edge of LAP with moderately large, deeply concave tentacle notch.

Inner side of LAP with relatively small, sharply defined, prominent and very slender ridge; ventral part of ridge strongly bent ventro-proximalwards, not merged with non-thickened ventral portion of LAP; dorsal part of ridge straight, strongly oblique, slightly widened dorsally; inner side of distal edge of LAP with two relatively small, well-defined, rounded, prominent spurs composed of densely meshed stereom; inner side of tentacle notch relatively small, deeply incised; sharply defined laterally. No perforations or furrows discernible.

Paratype supplements and variation

GZG.INV.78719 is a dissociated median LAP; nearly twice wider than high; ventral sixth slightly protruding ventro-proximalwards; ventro-distal tip of LAP very weakly protruding; spurs on proximal edge and outer surface ornament as in holotype. Three spine articulations similar to those observed on holotype. Ventral edge of LAP with small, weakly concave tentacle notch.

Inner side of LAP partly obscured by sediment; dorsal part of ridge exposed, as slender, straight, oblique as fine ridge observed on holotype; spurs on inner side of distal edge slightly better preserved than those of holotype.

GZG.INV.78720 is a dissociated distal LAP; more than three times wider than high; rod like; dorsal and ventral edges concave as a result of a constriction; proximal edge with two large, poorly defined, weakly prominent but very strongly protruding spurs. Four spine articulations, ventralmost similar to those observed on holotype, remaining three slightly larger and with conspicuous, lip-shaped, distal knob composed of densely meshed stereom. Tentacle opening invisible in external view, emerging on distal side of ventralmost spine articulation.

Inner side of LAP with two small, sharply defind, prominent knobs, proximal one horizontally slightly elongate, triangular, and distal one much smaller, round; inner side of distal edge of LAP with two poorly defined, prominent spurs. Large tentacle opening in the middle of the distal third of the LAP.

Remarks

These specimens display diagnostic characters that warrant inclusion in Dermacantha gen. nov., in spite of the unusually well-developed vertical striation on the outer surface and the well-defined spurs on the outer proximal and inner distal edges. On account of the latter, the LAPs in question can be unambiguously differentiated from any other currently known species of the genus. Greatest similarities are shared with an unnamed type of LAPs here assigned to Dermacantha gen. nov. from the Bajocian- Bathonian of France.As discussed in detail above, the Middle Jurassic LAPs are almost indistinguishable from the present ones, with possible differences pertaining to minor and potentially variable details in LAP morphology. Since the above-described Late Jurassic LAPs are represented by numerous wellpreserved specimens, they are formally described as new species of Dermacantha gen. nov. The Middle Jurassic record, in contrast, is described as probably new, but remains specifically unnamed.

The presence of lip-shaped distal knobs in the three dorsal spine articulations of the distal LAP described above is intriguing. Similar knobs are known from the distal LAPs of Early Jurassic Inexpectacantha acrobatica Thuy, 2011 and of extant Ophiolycus purpureus (Düben & Koren, 1846) and Ophiura (Ophiuroglypha) robusta (Ayres, 1854) (Thuy 2011; Thuy & Stöhr 2011). Remarkably, in all cases the lip-shaped knobs are associated with specialised, hook-shaped spines, which suggests that distal arm segments of Dermacantha carli sp. nov. bore such spines as well.

Occurrence

Late Oxfordian to early Kimmeridgian of Germany.

Figures

Fig. 30. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1-3. Dermacantha sp. nov. innom. from the Bajocian-Bathonian boundary of Touert, France. 1. GZG.INV.78714, proximal LAP. 2. GZG.INV.78715, median LAP. 3. GZG.INV.78716, distal LAP. 4-6. Dermacantha carli gen. et sp. nov. from the late Oxfordian (Late Jurassic) of the Plettenberg, Germany. 4. GZG.INV.78718 (holotype), proximal LAP. 5. GZG.INV.78719 (paratype), median LAP. 6. GZG. INV.78720 (paratype), distal LAP. 7-9. Ishidacantha hirokoae gen. et sp. nov. from the middle Toarcian (Early Jurassic) of Le Clapier, France. 7. GZG.INV.78723 (holotype), proximal LAP. 8. GZG.INV.78724 (paratype), median LAP. 9. GZG.INV.78725 (paratype), distal LAP. One common scale bar per species.