Ishidacantha hirokoae, 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 : 172-173

Ishidacantha hirokoae sp. nov.

urn:lsid:zoobank.org:act:CD39B010-D3BF-4BFA-9913-863830744D67

Fig. 30 : 7-9

p.p. Sinosura brodiei – Kutscher 1996: 10, pl. 2 figs 9-13. — Kutscher & Villier 2003: 185, pl. 4 figs 3-6 [material incorrectly assigned to Sinosura brodiei (Wright, 1866) ].

Diagnosis

Species of Ishidacantha gen. nov. with large LAPs displaying a well-developed, regular vertical striation on distal half of outer surface and composed of overlapping lamellae; two poorly developed spurs on outer proximal edge paralleled by two small, slightly better-defined spurs on inner distal edge; three moderately large, nearly equal-sized spine articulations proximally sharply delimited by distalmost lamellae; ventral and dorsal lobes of spine articulations separated by two or three small, notches; inner side of proximal LAPs with dorso-proximalwards bent, continuous proximal ridge and round distal knob; tentacle notch relatively small.

Etymology

Species named in honour of Hiroko Ishida, for her outstanding hospitality.

Type material

Holotype GZG.INV.78723 .

Paratype

GZG.INV.78724 and GZG.INV.78725.

Type locality and horizon

Le Clapier, France; debris flow bed rich in skeletal detritus, middle Toarcian, Early Jurassic.

Additional material

GZG.INV.78726 (18 dissociated LAPs) from sample 1 of the middle Toarcian of Le Clapier; GZG. INV.78727 (11 dissociated LAPs) from sample 2 of the middle Toarcian of Le Clapier; the original material of Kutscher (1996) and Kutscher & Villier (2003).

Description

Holotype

GZG.INV.78723 is a dissociated, large, proximal LAP; approximately twice wider than high; dorsal edge strongly concave as a result of a well-developed constriction; distal edge convex with a small, non-prominent protrusion; ventral half of LAP strongly protruding ventro-proximalwards, very large and wide; ventro-distal tip of LAP protruding, tongue shaped; ventro-proximal tip of LAP oblique; proximal edge of LAP with two very poorly defined, weakly prominent, very slender, non-protruding and horizontally elongate spurs; outer surface with well-developed, regular vertical striation composed of overlapping lamellae; strong proximalward decrease in size of lamellae; vertical striation replaced by finely meshed stereom on proximal half of outer surface. Three relatively small, nearly equal-sized and equi-distant, ear-shaped spine articulations freestanding on elevated distal portion of LAP; dorsal and ventral lobes of spine articulations separated by two or three very small notches; spine articulations proximally sharply delimited by two distalmost lamellae; gap between spine articulations and distal edge of LAP almost as wide as one spine articulation. Ventral edge of LAP nearly straight, except for extremely deeply incised, relatively small, more than semi-circular tentacle notch.

Inner side of LAP slightly obscured by sediment, with two closely spaced, but separate ridges; proximal one sharply defined, relatively broad, prominent and dorso-proximalwards bent ridge devoid of thickened parts or sharp kinks; distal ridge very short, knob like, sharply defined and moderately widely separated from proximal ridge; inner side of distal edge of LAP with small, moderately well-defined, weakly prominent, very slender, horizontally elongate. No perforations or furrow discernible.

Paratype supplements and variation

GZG.INV.78724 is a dissociated median LAP; slightly more than twice wider than high; very well in agreement wth holotype; vertical striation on outer surface slightly less well developed and regular as in holotype. Three spine articulations similar to those observed on holotype. Tentacle notch slightly not as deep as in holotype.

Inner side of LAP with two ridges similar to those of holotype but more widely separate, and proximal one shorter and with slightly widened ventral tip; two spurs on inner side of distal edge of LAP shorter than in holotype. No perforations or furrow discernible.

GZG.INV.78725 is a dissociated distal LAP; approximately 2.5 times wider than high; well in agreement with holotype; vertical striation on outer surface better developed than in holotype, replaced by finely meshed stereom only on proximal quarter of outer surface. Three spine articulations similar to those observed on holotype. Ventral edge of LAP slightly concave; tentacle opening developed as perforation emerging on ventral edge of ventralmost spine articulation.

Inner side of LAP obscured by sediment.

Remarks

These specimens appear to be identical to at least part of the LAPs described and illustrated by Kutscher (1996) and Kutscher & Villier (2003) from the Toarcian/Aalenian of Germany and the Toarcian of France, respectively, and assigned in both cases to the ophioleucinid Sinosura brodiei (Wright, 1866) . A re-examination of the type material of the latter (see Hess 1964), however, has revealed fundamental differences in LAP morphology, in particular with respect to spine articulation morphology. The LAPs in question show clear ophiacanthid affinities and, as discussed above, are here considered to belong to the same LAP type as the material described as Ophiopholis ? trispinosa Hess, 1965 from the Oxfordian of France, for which Ishidacantha gen. nov. is here introduced. Within this genus, these LAPs are unique in combining three equal-sized spine articulations with a well-developed vertical striation on outer surface and two poorly defined spurs on the outer proximal edge. They are thus described here as a new species.

Kutscher (1996) and Kutscher & Villier (2003) mentioned up to six spine articulations in their descriptions of the above-mentioned LAPs. The specimens illustrated, however, invariably show three spine articulations just like the Toarcian material of France described here. Thus, it seems probable that Kutscher (1996) and Kutscher &Villier (2003) included more than one LAP type in their descriptions.

Occurrence

Middle Toarcian of France, Toarcian/Aalenian 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.