Rafinesquina (Mesogeina) gabianensis, Colmenar, 2016

Colmenar, Jorge, 2016, Ordovician rafinesquinine brachiopods from peri-Gondwana, Acta Palaeontologica Polonica 61 (2), pp. 293-326 : 311-314

Rafinesquina (Mesogeina) gabianensis sp. nov.

Figs. 12 , 13 .

Etymology: After the Gabian Formation, from where the type material comes.

Type material: Holotype: MPZ 2015 /1387, external and internal moulds of dorsal valve ( Fig. 13A ) . Paratypes: MPZ 2015 /1382–1386, MPZ 2015 /1388, 1389.

Type locality: Tranchée Noire ( Havlíček 1981), abandoned railway cutting close to the Gabian village, Montagne Noire ( France) .

Type horizon: Alternating marlstone and bioclastic limestone beds of the lower part of the Gabian Formation, middle–upper Katian (Ka2–4 stage slices), Upper Ordovician.

Material.—Internal and external moulds of 22 ventral valves and 15 dorsal valves; MPZ 2015 /1526–1554 from the type locality and horizon .

→ Fig. 10. Rafinesquinine brachiopod Kjaerina (Villasina) pyrenaica sp. nov. (A–H) from lower–middle Katian (Ka1–2), Upper Ordovician, Cavá Formation, Pyrenees, Spain and Kjaerina (Villasina) cf. pyrenaica (I–K) from Katian, Upper Ordovician , Bruncu de is Mallorus Member of the Punta Serpeddi Formation, Sardinia, Italy . A. MPZ 2015 /1372, holotype, internal mould of ventral valve in upper (A 1) and lateroblique (A 2) views. B . MPZ 2015 /1373, paratype, latex cast of exterior of a ventral valve. C . MPZ 11579 , paratype, internal mould of ventral valve. D . MPZ 11580 , paratype, internal mould of ventral valve. E . MPZ 11578 , paratype, internal mould of ventral valve. F . MPZ 2015 /1374, paratype, latex cast of dorsal valve (F 1) and anteroblique view of cardinalia (F 2). H . MPZ 11582 , paratype, latex cast of exterior of an incomplete dorsal valve. G . MPZ 2015 /1375, paratype, latex cast of interior (G 1) and exterior (G 2) of a dorsal valve. I . MPZ 2015 /1376, latex cast of exterior of a ventral valve. J . MPZ 2015 /1377, latex cast of exterior of a ventral valve. K . MPZ 2015 /1378, latex cast of exterior of a ventral valve. Scale bars 2 mm .

Diagnosis.—Species of Rafinesquina (Mesogeina) with shell slightly wider than long, often with weakly alate cardinal extremities. Ventral valves evenly convex, about 18% as deep as long and gently convex dorsal valves. Radial ornament with 4–6 ribs per 2 mm at 10 mm anteromedially from umbo, with up to three costellae between two costae; concentric ornament filate. Cardinal process lobes with concave and smooth myophores in adult specimens; notothyrial platform low, strongly reduced.

Description.—Shell of medium to large size (largest specimen 32.8 mm wide), concavoconvex, semicircular in outline; maximum valve width at hinge; slightly acute cardinal angles. Ventral valve evenly convex, 68–109% as long as wide (x = 89%; n = 8; σn = 0.15) and 15–22% as deep as long x = 18%; n = 3; σn = 0.003). Ventral interarea planar, apsacline, very short, 3% as long as valve length, delthyrium with apical pseudodeltidium. Dorsal valve approximately

77% as long as wide (x = 14%; n = 4; σn = 0.003) and with gently concave lateral profile; dorsal interarea anacline, about 4% as long as valve length; chilidium not observed.

Radial ornament unequally parvicostellate, with commonly 6 ribs per 2 mm at 10 mm anteromedially from umbo but occasionally with only 4 or 5, all of them with rounded crests. Concentric ornamentation consisting of fine fila, with counts of 11 per mm, intersecting the radial ornament; some specimens show evidences of shell damage, reflected as discontinuities in the shell ornament ( Fig. 12A, B, E ).

Ventral interior with teeth triangular in section, dental plates short, straight, extending forward approximately 8% of valve length and with average dental plates divergence angle of 98° (range 75–109°; n = 10); muscle field poorly impressed anteriorly, subtriangular to flabelliform, approximately 35% as wide as maximum valve width and surrounded posterolaterally by very narrow and thin muscle bounding ridges. Adductor scar lanceolate located between diductor scars and approximately 20% as wide as muscle scar maximum width.

Dorsal interior with thin and about 95° divergent socket ridges bounding posteriorly triangular dental sockets; bifid cardinal process, with ventrally divergent, elongate or plate-like lobes in young specimens ( Fig. 13B ), but triangular in outline and ponderous in adult specimens ( Fig. 13A ); the lobes are weakly divergent anteriorly and the myophores has a concave posteroventral surface; notothyrial platform, low, very reduced, continuous anteriorly with broad and low median ridge halving the poorly impressed dorsal muscle field. Pseudopunctae visible in both interiors, with radial regular arrangement over the entire shell excepting posterolaterally where exhibit a more irregular pattern. Ornamentation, both radial and concentric, impressed in interior of both valves.

Remarks.—Among all the species of this subgenus, the new species is most similar to Rafinesquina (Mesogeina) pomoides Havlíček, 1971 from the Upper Ordovician of Morocco and the Iberian Chains, in having a very convex ventral valve. As noted above, the new species has a very convex ventral valve about 14% as depth as long, but these values are lower than those of R. (Mesogeina) pomoides ventral valves, up to 27% as deep as long. Other characters that allow differentiating R. (Mesogeina) gabianensis from the Moroccan species are the absence of geniculation in R. (Mesogeina) gabianensis and the more alate cardinal extremities and the lower rib density of the new species, up to 6 ribs per 2 mm at 10 mm anteromedially from umbo in spite of 8–10 at the same growth stage of the Moroccan species. Finally the new species has concave myophores and a very small notothyrial platform whereas in R. (Mesogeina) pomoides the posteroventral surface of the myophores is flat and the notothyrial platform is much better developed.

Stratigraphic and geographic range.— Type locality and horizon only.

Figures

Fig. 12. Ventral valves of rafinesquinine brachiopod Rafinesquina (Mesogeina) gabianensis sp. nov.; middle–upper Katian (Ka2–4), Upper Ordovician; Gabian Formation, Montagne Noire, France. A. MPZ 2015/1382, paratype, internal mould (A1) and latex cast of interior (A2) and exterior (A3). B. MPZ 2015/1383, paratype, internal mould (B1) and latex cast of exterior (B2) of a complete valve. C. MPZ 2015/1384, paratype, internal mould. D. MPZ 2015/1385, paratype, internal mould. E. MPZ 2015/1386, paratype, internal mould (E1) and latex cast of exterior (E2) of a small valve. Scale bars 2 mm.

Fig. 13. Dorsal valves of rafinesquinine brachiopod Rafinesquina (Mesogeina) gabianensis sp. nov.; middle–upper Katian (Ka2–4), Upper Ordovician; Gabian Formation, Montagne Noire, France. A. MPZ 2015/1387, holotype, latex cast of interior (A1), detail of cardinalia in anteroblique (A2) and posteroblique (A3) views, dorsal exterior (A4). B. MPZ 2015/1388, paratype, latex cast of interior (B1), detail of cardinalia in anteroblique (B2) and posteroblique (B3) views of a small specimen. C. VMN-1.22, paratype, latex cast of exterior. Scale bars 2 mm.