Kjaerina (Villasina) pyrenaica, Colmenar, 2016

Colmenar, Jorge, 2016, Ordovician rafinesquinine brachiopods from peri-Gondwana, Acta Palaeontologica Polonica 61 (2), pp. 293-326 : 307-309

Kjaerina (Villasina) pyrenaica sp. nov.

Fig. 10A–H.

1970 Rafinesquina sp. ; Hartevelt 1970: 174. Etymology: After the Pyrenees Mountains.

Type material: Holotype: MPZ 2015 /1372, internal mould of ventral valve (Fig. 10A) . Paratypes: MPZ 11577–11580 , 11582 ; MPZ 2015 /1373–1375.

Type locality: Seo de Urgel , Spanish Pyrenees .

Type horizon: Thickly bedded sandstone of the Cavá Formation , lower –middle Katian (Ka1–2), Upper Ordovician .

Material.—Internal and external moulds of 11 ventral valves and eight dorsal valves; MPZ 2015 /1516–1525 from the type locality and horizon .

Diagnosis.—Species of Kjaerina (Villasina) with ventral valve disc moderately convex. Dorsal valve disc flat to concave with shallow median sulcus; both, ventral and dorsal valve trails, inclined with respect to disc about 90°; chilidium unknown. Radial ornament with 4–5 ribs per 2 mm at 10 mm anteromedially from umbo; prominent median rib absent; strong and irregular rugae covering the entire disc, better developed posterolaterally. Muscle bounding ridges curved interiorly; ventral muscle field well impressed, elongate, flabelliform. Cardinal process lobes, plate-like in young specimens, engrossed postero ventrally in adult ones; notothyrial platform strong; broad median ridge.

Description.—Shell of medium to large size (largest specimen 30.8 mm wide), concavoconvex, both valves strongly geniculate dorsally; semicircular in outline, or weakly alate in some specimens; maximum valve width at hinge line; slightly acute to rectangular cardinal angles. Ventral valve ranging 71–102% as long as wide (x = 90%; n = 4; σn = 0.13) and 13–14% as deep as long (x = 14%; n = 4; σn = 0.003); longitudinal profile strongly geniculate dorsally with moderately convex disc forming an angle about 90° with trail ranging 45–65% as long as valve length. Ventral interarea planar, apsacline, 7% as long as valve length, delthyrium with apical pseudodeltidium. Dorsal valve with longitudinal profile strongly geniculate dorsally with flat to concave disc with shallow median sulcus, forming an angle about 90° with trail ranging 45–65% as long as valve length; dorsal interarea anacline; notothyrium filled completely by cardinal process. Chilidium unknown.

Radial ornament multicostellate with 4–5 ribs per 2 mm at 10 mm anteromedially from umbo, all of them with rounded crests; no prominent median costa. Concentric ornamentation of fila and strong irregular rugae, covering entire disc but better developed on posterolateral sides of valves where run oblique to hinge line.

Ventral interior with straight, short, blade-like dental plates extending forward approximately 10% of valve length and with average dental plates divergence angle of 95° (range 77–113°; n = 6); muscle field very well impressed, elongate, flabelliform ranging 55–61% as long as valve length, 25–51% as wide as maximum valve width and completely surrounded laterally by inwardly curved muscle bounding ridges.

Dorsal interior with strong socket ridges, diverging anteriorly about 85° and bounding triangular dental sockets; bifid cardinal process with elongate or plate-like lobes in young specimens (Fig. 10G), but engrossed in postero-ventral direction in gerontic specimens. The lobes are weakly divergent anteriorly and are situated on thick, anchor-shaped notothyrial platform, continuous anteriorly with broad median ridge halving dorsal muscle field. Shell structure unobservable due to grain size.

Remarks.—The ventral muscle field outline of this species resembles the one known from the species of Kiaeromena , but the multicostellate radial ornament, the less coarse rugation, as well as all the main dorsal internal characters differentiate this leptaenine genus from Kjaerina (Villasina) . Especially the cardinal process, the straight socket ridges, not curving inwardly to bound the dorsal muscle scars and the absence in the studied material of transmuscle ridges. This new species clearly differs from the other Kjaerina (Villasina) species in having a very low ribs density, 4–5 ribs per 2 mm counted at 10 mm anteromedially from umbo (K. [Villasina] almadenensis has 6–8 at the same growth stage, K. [Villasina] meloui has 9–12 and K. [Villasina] pedronaensis 7–8 ribs), and by having a shallow dorsal median sulcus, autapomorphy of this species. Hartevelt (1970) cited the presence of Rafinesquina sp. in the Cavá Formation, probably referring to shells included now within this new species.

Stratigraphic and geographic range.— Type locality only.