Kjaerina (Villasina) meloui, Colmenar, 2016

Colmenar, Jorge, 2016, Ordovician rafinesquinine brachiopods from peri-Gondwana, Acta Palaeontologica Polonica 61 (2), pp. 293-326 : 304-306

Kjaerina (Villasina) meloui sp. nov.

Fig. 7.

1975 Rafinesquina sp. ; Mélou and Plusquellec 1975: 15.

1985 Hedstroemina sp. C ; Young 1985: 350, pl. 36: 1–10.

1990 Hedstroemina cf. fragilis Bancroft, 1929 ; Mélou 1990: 554, text-fig. 7, pl. 9: 1–8.

Etymology: Species dedicated to Michel Mélou for his contributions in the study of the Ordovician brachiopods.

Type material: Holotype: MPZ 2015 /1353, internal mould of dorsal valve (Fig. 7A) . Paratypes: LPB 17191–17195 , MPZ 2015/1354.

Type locality: Lime kiln quarry, île de Rosan, Crozon ( Finistère , France) .

Type horizon: Stratigraphic layer 16 of the Tufs et Calcaires de Rosan Formation, upper Katian (Ka3–4 stage slices) .

Material.—Internal and external moulds of two ventral valves and 13 dorsal valves; MPZ 2015 /1501–1508 from the type locality and horizon .

Diagnosis.— Kjaerina (Villasina) species with ventral valve disc slightly convex.Dorsal valve disc flat to concave.Radial ornament with 9–12 ribs per 2 mm at 10 mm anteromedially from umbo; prominent median rib absent; irregular rugae development. Cardinal process stout; myophores with striated posteroventral surface; mesocardinal ridge always present; notothyrial platform strongly reduced; median ridge long and narrow; transmuscle septa narrow, longer than median ridge; dorsal median breviseptum, narrow, often present.

Description.—Shells of large size (largest specimen 50 mm wide), concavoconvex, with dorsally directed geniculation, semicircular in outline, maximum valve width at hinge line in young specimens and slightly anteriorly in older ones; acute cardinal angles in early growth stages, rectangular to slightly obtuse in adult stages. Ventral valve 80% as long as wide; lateral profile geniculate dorsally, at approximately 25 mm long growth stage, with slightly convex disc and with variable trail length; ventral interarea planar, apsacline, 8% as long as valve length; delthyrium open. Dorsal valve lateral profile geniculate dorsally with flat to concave disc and with variable trail length; dorsal interarea planar, anacline, 6% as long as valve length; notothyrium filled completely by cardinal process; medially grooved convex chilidium, as long as dorsal interarea length, covering up to 50% of cardinal process lobes.

Radial ornament multicostellate with 9–12 ribs per 2 mm at 10 mm anteromedially from umbo and without prominent median rib, all of them with rounded crests, small

Fig. 7. Rafinesquinine brachiopod Kjaerina (Villasina) meloui sp. nov.; upper Katian (Ka3–4), Upper Ordovician ; upper part of Rosan Formation, → Armorican Massif, France. A. MPZ 2015 /1353, holotype, latex cast of dorsal interior in upper view (A 1), lateroblique view of a dorsal valve (A 2), details of cardinalia in anteroblique (A 3), and posteroblique (A 4) views, dorsal exterior (A 5). B. LPB-17192 , paratype, latex cast of dorsal interior in upper view B 1), details of cardinalia in anteroblique (B 2) and posteroblique (B 3) views of dorsal valve. C–E. Paratypes, details of cardinalia of a dorsal valves .

C. LPB-17194 . D. MPZ 2015 /1354. E. LPB-17195 . F. LPB-17193 , paratype , latex cast of exterior of a dorsal valve. G. LPB-17191 , paratype , internal mould (G 1) and latex cast of interior (G 2) of a ventral valve. Scale bars 2 mm.

intercostal spaces; concentric ornament of fila and irregular impersistent rugae well developed in the posterolateral sides of the disc and with wave length of about 1 mm.

Ventral interior with divergent, thin, blade-like dental plates extending forward approximately 7% of valve length and average dental plates divergence angle of 80°, continuous anteriorly with curved inwardly muscle bounding ridges; ventral muscle field triangular to flabellate, with divergent diductor scars not enclosing anteriorly narrow adductor scars; myophragm present posteriorly to adductor scars.

Dorsal interior with tabular, thin and divergent socket ridges bounding triangular dental sockets; bifid cardinal process with plate-like and weakly divergent lobes on a reduced notothyrial platform that continues anteriorly with long, narrow median ridge; porteroventral surface of myophores striated longitudinally; in adult specimens lobes become ponderous; between lobes, mesocardinal ridge supporting chilidium always present. Dorsal muscle field weakly elongated, crossed by long transverse transmuscle septa; thin dorsal median breviseptum often present anteriorly to median ridge. Both valves with very fine pseudopunctae, regularly arranged all over the shell, coinciding with intercostal spaces.

Remarks.—This species resembles in many characters K.

Hedstroemina ) fragilis ( Bancroft, 1929) as Mélou (1990) noted when referred provisionally the Armorican specimens to this species, but the multicostellate ornament of these shells allows a ready discrimination from the parvicostellate British species, as well as its inclusion in the new subgenus Kjaerina (Villasina) . The high ribs density with 9–12 ribs per 2 mm at 10 mm anteromedially from umbo, K.

Villasina) almadenensis has 6–8 at the same growth stage, their weaker rugae development, the thin and long median ridge and the dorsal median breviseptum, are significant enough differences to erect a new species.

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