Ophiolimna malagasica, 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 : 67-69

Ophiolimna malagasica sp. nov.

urn:lsid:zoobank.org:act:158198F0-5105-4FD2-94F3-F79984D38A0E

Fig. 13 : 9-12

Diagnosis

Species of Ophiolimna with tiny LAPs displaying pointed, strongly ventro-proximalwards protruding ventral portion (accounting for at least one-third of the total height of proximal LAPs); outer surface almost entirely covered by relatively coarse vertical striation; up to six relatively large spine articulations separated from distal edge of LAP by very narrow gap; inner side with spoon-shaped central ridge with strongly widened, round dorsal tip, and second ventral, triangular ridge.

Etymology

Name formed after the Malagasy Gulf which formed a southerly extension of the Tethys between Africa and India in Jurassic times, in reference to the origin of the type material.

Type material

Holotype GZG.INV.78553 .

Paratypes

GZG.INV.78554, GZG.INV.78555 and GZG.INV.78556.

Type locality and horizon

Jumara, Kachchh, India; sample 24, Patcham Formation, late Bathonian, Middle Jurassic.

Additional material

GZG.INV.78557 (5 dissociated LAPs) from sample 24; GZG.INV.78558 (13 dissociated LAPs) from sample 15; GZG.INV.78559 (6 dissociated LAPs) from sample 31; GZG.INV.78560 (8 dissociated LAPs) from sample 89.

Description

Holotype

GZG.INV.78553 is a dissociated, minute, very fragile, proximal LAP; considerably higher than wide; dorsal edge fragmentary; distal edge slightly convex; preserved portion of proximal edge undulose, devoid of spurs; ventral portion of LAP pointed, strongly protruding ventro-proximalwards, accounting for at least one-third of the total LAP height; outer surface almost entirely covered by coarse, regular, vertical striation composed of broad, overlapping lamellae decreasing in size distalwards and replaced by finely meshed stereom only at the very proximal edge of the LAP. Six relatively large, ear-shaped, equi-distant spine articulations in notches of the distal edge, overlapped by the undulose distalmost lamella; ventral lobe large, conspicuously tongue shaped and connected with the distalmost lamella in all spine articulations; strong dorsalward increase in size of spine articulations; very narrow gap between spine articulations and distal edge of LAP. Ventral edge of LAP strongly oblique on account of the pointed ventral portion, with large, concave tentacle notch.

Inner side of LAP with conspicuous, sharply defined, prominent, spoon-shaped central ridge displaying strongly widened, round and proximally pointing dorsal tip and very slightly widened ventro-distally pointing ventral tip; second sharply defined, strongly prominent, triangular ridge close to the centre of the ventro-distal edge of the LAP; no spurs discernible on inner side of distal edge of LAP. No perforations discernible.

Paratype supplements and variation

GZG.INV.78554 is a dissociated median LAP; nearly as wide as high, dorso-proximal edge strongly fragmentary; ventral third to quarter strongly protruding ventro-proximalwards; lamellae of outer surface vertical striation very coarse. Four equidistant spine articulations with slight dorsalward increase in size. Inner side well in agreement with that of holotype; dorsal tip of central ridge less strongly widened.

GZG.INV.78555 is a dissociated distal LAP of rounded rectangular outline, slightly wider than high; dorsal edge straight; proximal edge intact, slightly undulose, devoid of spurs; ventral portion of LAP hardly protruding ventro-proximalwards. Four equidistant and nearly equal-sized spine articulations in notches of distal edge. Ventral edge of LAP convex with small, concave tentacle notch next to ventralmost spine articulation.

Inner side of LAP largely obscured by sediment; dorsal tip of central ridge discernible, only slightly widened, proximalwards pointing; no ventral ridge discernible.

GZG.INV.78556 is a dissociated median LAP; proximal edge completely intact, slightly undulose with narrow band of finely meshed stereom, otherwise well in agreement with other type specimens.

Remarks

The tiny LAPs described above are so strikingly similar to those of extant species of Ophiolimna , showing all the diagnostic LAP-morphological characters of the genus, that assignment to Ophiolimna seems unquestionable. Among the species assigned to Ophiolimna , the closest similarities are shared with Ophiolimna kucerai sp. nov. (see below). In the latter, however, the LAPs are larger and display a larger gap between the spine articulations and the distal edge.

Occurrence

Middle Bathonian to Callovian of India.

Figures

Fig. 13. Lateral arm plates (LAPs) of fossil and Recent ophiacanthid brittle stars in external (a) and internal (b) views. 1-3. Ophiotoma incredibilis sp. nov. from the latest Aptian to earliest Albian (Early Cretaceous) of Blake Nose, NE Atlantic. 1. GZG.INV.78549 (holotype), proximal LAP. 2. GZG. INV.78550 (paratype), median LAP. 3. GZG.INV.78551 (paratype), distal LAP. 4. Ophiolimna antarctica (Lyman, 1879), Recent, proximal LAP. 5-6. Ophiolimna perfida (Koehler, 1904), Recent. 5. Proximal LAP. 6. distal LAP. 7-8. Ophiolimna tiamatia sp. nov. from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 7. NHMW 2012/0137/0010 (holotype), proximal LAP. 8. NHMW 2012/0137/0011 (paratype), median LAP. 9-12. Ophiolimna malagasica sp. nov. from the Bathonian (Middle Jurassic) of Jumara, India. 9. GZG.INV.78553 (holotype), proximal LAP. 10. GZG.INV.78554 (paratype), median LAP. 11. GZG.INV.78555 (paratype), median LAP. 12. GZG. INV.78556 (paratype), distal LAP. One common scale bar per species is given.