Lapidaster varuna, 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 : 37-39

Lapidaster varuna sp. nov.

urn:lsid:zoobank.org:act:6E723392-8565-4F6C-84C5-B6FEBE1A69CB Fig. 8 : 5-7

Diagnosis

Species of Lapidaster gen. nov. with relatively large LAPs displaying a weakly to moderately welldeveloped vertical striation, a long ridge on the inner side reaching the dorsal edge of the LAP, and up to four spine articulations composed of confluent dorsal and ventral lobes.

Etymology

Species named after Varuna, the god of the oceans in Hindu mythology, in reference to the cultural background prevailing in the area of the type locality in Kachchh, India.

Type material

Holotype GZG.INV.78511 .

Paratypes

GZG.INV.78512 and GZG.INV.78513.

Type locality and horizon

Jumara, Kachchh, India; sample 117, upper Chari Formation, Callovian, Middle Jurassic.

Additional material

GZG.INV.78514 (78 dissociated LAPs) from sample 117; GZG.INV.78515 (14 dissociated LAPs) from sample 119; GZG.INV.78516 (12 dissociated LAPs) from sample 121.

Description

Holotype

GZG.INV.78511 is a dissociated, medium-sized, median to proximal LAP, slightly wider than high; dorsal and distal edges straight to slightly convex; ventral quarter of LAP protruding ventroproximalwards; ventro-distal tip of LAP strongly protruding, tongue shaped; proximal edge evenly concave, with small, rather poorly defined and slightly prominent spur near ventro-proximal tip of LAP; outer surface consisting of coarsely meshed stereom with trabeculae merging into irregular vertical striation, especially near spine articulations; coarsely meshed stereom rapidly grading into much more finely meshed stereom near proximal edge of LAP. Three equal-sized spine articulations near distal edge of LAP, ventral and dorsal lobes forming continuous volute; two ventral spine articulations surrounded by irregular areole of finely meshed stereom; dorsalmost spine articulation embedded in striated to coarsely meshed stereom, separated from two ventral spine articulations by slightly larger gap. Ventral edge of LAP with large, very deep and concave tentacle notch.

Inner side of LAP with sharply defined, prominent and relatively narrow ridge, dorsal portion of which oblique, nearly straight, with slightly widened, round tip, almost reaching dorso-proximal corner of LAP; ventral portion of ridge separated from dorsal one by slightly round kink, much less sharply defined and rapidly merging into thickened ventral part of LAP. Inner distal edge of LAP thinning out distalwards, with small, sharply defined, lens-shaped spur composed of compact stereom on inner ventro-distal tip of LAP. Inner side of tentacle notch with coarsely meshed and slightly horizontally stretched stereom, dorsally bordered by large, irregular perforation.

Paratype supplements and variation

GZG.INV.78512 is a dissociated proximal LAP, nearly as wide as high; dorsal and distal edges gently convex; ventral quarter of LAP and ventro-distal tip largely missing; spur on outer proximal edge slightly protruding, otherwise well in agreement with corresponding spur observed on holotype; outer surface with coarsely meshed stereom merged into faint vertical striation. Four spine articulations, ventralmost smaller than remaining three; dorsalward increase in size of gaps separating spine articulations; three ventral spine articulations surrounded by irregular areole.

Inner side of LAP well in agreement with that of holotype; dorsal portion of ridge slightly shorter, not approximating dorso-proximal corner of LAP.

GZG.INV.78513 is a dissociated distal LAP, approximately twice wider than high; dorsal edge slightly concave; distal edge straight; ventral fifth of LAP protruding ventro-proximalwards; ventro-distal tip of LAP strongly protruding, tongue shaped; proximal edge nearly straight, with sharp kink in ventral quarter, marked by well-defined, elongate, slightly prominent and protruding spur composed of very dense stereom; outer surface with coarsely meshed stereom with trabeculae showing only very faint tendency to merge into vertical striation. Three spine articulations, middle one slightly larger than ventral and dorsal ones. Tentacle notch large and moderately deep.

Inner side well in agreement with than of holotype; dorsal portion of ridge not reaching dorso-proximal corner of LAP, not widened at dorsal tip.

Remarks

These LAPs display a striking similarity to those of extant Ophiologimus hexactis H.L. Clark, 1911 , but differ in having a spur on the outer proximal and inner distal edges. Although this spur is rather poorly developed, the present LAPs are assigned to Lapidaster gen. nov. Within this genus, closest similarities are shared with Lapidaster fasciatus comb. nov., in which, however, the LAPs have a much better-developed vertical striation and a slightly shorter ridge on the inner side. These differences, even if seemingly small, are considered sufficient for distinction at the species level, in accordance with the observations of Thuy & Stöhr (2011) on the spectrum of possible differences in LAP morphology between congeneric species. The present LAPs are therefore described as a new species.

Occurrence

Callovian of India.

Figures

Fig. 8. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views. 1. Lapidaster sp. nov. innom. 1 from the late Toarcian (Early Jurassic) of Seewen, Switzerland; NHMB M11208, proximal to median LAP. 2-4. Lapidaster wolfii gen. et sp. nov. from the Bajocian-Bathonian boundary (Middle Jurassic) of Touert, France. 2. GZG.INV.78508 (holotype), proximal LAP. 3. GZG. INV.78509 (paratype), median LAP. 4. GZG.INV.78510 (paratype), distal LAP. 5-7. Lapidaster varuna gen. et sp. nov. from the Callovian of Jumara, India. 5. GZG.INV.78511 (holotype), proximal LAP. 6. GZG.INV.78512 (paratype), median LAP. 7. GZG.INV.78513 (paratype), distal LAP. One common scale bar per species is given.