Kjaerina (Kjaerina) gondwanensis, Colmenar, 2016

Colmenar, Jorge, 2016, Ordovician rafinesquinine brachiopods from peri-Gondwana, Acta Palaeontologica Polonica 61 (2), pp. 293-326 : 296-297

Kjaerina (Kjaerina) gondwanensis sp. nov.

Figs. 2, 3.

1985 Hedstroemina sp. A ; Young 1985: 342, pl. 32: 1–13.

2013 Hedstroemina sp. ; Colmenar et al. 2013: 159, fig. 4A–I. Etymology: After the Gondwana supercontinent, where Mediterranean shelves were inhabited by this species.

Type material: Holotype: MPZ 2015 /1335, external mould of ventral valve (Fig. 2A 1) . Paratypes: MPZ 2015 /1336–1345, VOMN 2200, MNHN.F.A46450–46456.

Type locality: “Sa Siliqua”, locality (Gon 1, see Hammann and Leone 1997: text-fig. 8 for exact location), Gonnessa , province of Carbonia- - Iglesias, Sardinia, Italy .

Type horizon: Grey siltstone of the lower part of Portixeddu Formation, upper Berounian (lower–middle Katian, Ka1–2 stage slices).

Material. —Internal and external moulds of 39 ventral valves and 10 dorsal valves; MPZ 2015/1471–1500 from Gon1 locality, lower–middle Katian (Ka1–2).

Diagnosis. —Species of Kjaerina (Kjaerina) with variable outline during ontogeny from alate to semicircular; longitudinal profile concavoconvex. Radial ornament unequally parvicostellate with 5–8 ribs per 2 mm at 10 mm from umbo, often with prominent median rib; variable development of rugae, normally restricted to posterolateral extremities. Ventral muscle field triangular faintly impressed and without muscle bounding ridges.

Description. —Shells of medium to large size (largest specimen 31 mm wide), lateral profile concavoconvex; changing from weakly alate to semicircular in outline through ontogeny; maximum valve width at hinge line in most specimens, and more rarely slightly anteriorly to hinge line; slightly acute to rectangular cardinal angles and rectimarginate anterior commissure. Ventral valve ranging 62–130% as long as wide (x = 83%; n = 31; σn = 0.16) and 5–20% as deep as long (x = 10%; n = 23; σn = 0.04); in young specimens wider than long and vice versa in adult ones; moderately convex umbonal region and subplanar anteriorly, only one specimen with incipient dorsally directed geniculation at 17 mm long growth stage (Fig. 2E). Ventral interarea planar, apsacline, 6–13% as long as valve length, delthyrium with apical pseudodeltidium. Dorsal valve about 91% as long as wide and 9% as deep as long; with flat to slightly concave lateral profile. Dorsal interarea planar, anacline, about 2% as long as valve length; notothyrium covered by a medially grooved chilidium.

Radial ornament unequally parvicostellate with 5–8 ribs per 2 mm at 10 mm anteromedially from umbo, with up to 4–5 costellae intercalated between two costae; all of them with rounded crests; with prominent median costa in a few ventral valves. Concentric ornamentation of fila and variably developed discontinuous rugae, on posterolateral sides of valves, running oblique to hinge line; only a single specimen (Fig. 2H) with continuous rugae covering the entire valve.

Ventral interior with divergent, thin, blade-like dental plates extending forward approximately 10% of valve length and average dental plates divergence angle of 90° (range 79– 114°; n = 18); muscle field triangular, very poorly impressed and without muscle bounding ridges.

Dorsal interior with strong and divergent socket ridges bounding triangular and elongated dental sockets; bifid cardinal process with elongated or plate-like and weakly anteriorly divergent lobes on low notothyrial platform, continuous with broad median ridge (Fig. 3A); between the cardinal process lobes a mesocardinal ridge (see Pope 1976) supporting the chilidium is present in some specimens (Fig. 3E); dorsal muscle field weakly elongated, about 90% as long as wide (n = 1). Shell structure finely pseudo-punctate.

Remarks. —The study of abundant and well-preserved material from Sardinia, together with material from the Glauzy Formation (Montagne Noire, France) allows now the formal description of a new species of Kjaerina (Kjaerina) . Some specimens from the upper part of the Louredo Formation at Penha García Syncline ( Portugal) figured by Young (1985: pl. 32: 1–13) as Hedstroemina sp. A , which show the same features as the studied shells, have also been included within the new species.

The presence of only one specimen with an incipient geniculation at 17 mm long growth stage (Fig. 2E) and having other much larger and without geniculation (Fig. 2B), suggests that it is an exceptional feature for the species. In some aspects Kjaerina (Kjaerina) gondwanensis sp. nov. resembles several species of the subgenus. The accentuated central costella, for instance, is a common feature in all species of K. ( Kjaerina ) except for K. (Kjaerina) complanata and K. (Kjaerina) hartae . The mucronate cardinal extremities and the posterolateral rugae are characters shared only with K. (Kjaerina) typa typa and K. (Kjaerina) typa geniculata . Nevertheless the dental plates not extending forward as muscle bounding ridges allow discriminating the studied material from these two species. K. (Kjaerina) gondwanensis differs from K. (Kjaerina) hedstroemi in lesser extension of the dental plates, in its shell outline, and presence of rugae. The new species also differs from K. (Kjaerina) complanata and K. (Kjaerina) jonesi in its shell outline and the absence of rugae. Finally K. (Kjaerina) gondwanensis differs from K. (Kjaerina) bipartita in the absence of muscle bounding ridges and possessing mucronate cardinal extremities and rugae.

Stratigraphic and geographic range. — In addition to the type locality, K. (Kjaerina) gondwanensis also occurs in the upper part of the Glauzy Formation ( Ka 1–2) and in the Gabian Formation ( Ka 2–4), Montagne Noire ( France), as well as in the upper part of the Louredo Formation ( Sa 2– Ka 1), Penha García Syncline ( Portugal). Upper Sandbian–Katian .