Rafinesquina (Mesogeina) loredensis, Colmenar, 2016

Colmenar, Jorge, 2016, Ordovician rafinesquinine brachiopods from peri-Gondwana, Acta Palaeontologica Polonica 61 (2), pp. 293-326 : 314-316

Rafinesquina (Mesogeina) loredensis sp. nov.

Fig. 14 .

1985 Hedstroemina mundae (Sharpe, 1853) ; Young 1985: 345, pl. 34:

3, 8–9; non pl. 34: 1–2 (= Orthis? mundae ), 4–7 (= R. [ Mesogeina ] pseudoloricata ), 10 (K. [Villasina] almadenensis ). Etymology: After the name of the Loredo village. Type material: Holotype: IGM-2919, internal mould of ventral valve Fig. 14A ). Paratypes: IGM-2923, 2925–2927. Type locality: 250 m NE of the Louredo village, Aveiro district ( Portugal). Type horizon: Volcaniclastic rocks of the lower part of Porto de Santa Anna Formation, uppermost upper Berounian (probably middle Katian, Ka2 stage slice), Upper Ordovician at Louredo locality (Portuguese Central Iberian Zone).

Material.— Type material only.

Diagnosis.—Species of Rafinesquina (Mesogeina) with shell wider rather than long; ventral valves slightly convex, about 9% as deep as long and almost flat to slightly concave dorsal valves. Radial ornament with 6 ribs per 2 mm at 10 mm anteromedially from umbo, not clearly organized in sectors. Ribs subquadrate in section, twice as wide as the intercostal spaces. Ventral muscle field large, flabellate, poorly impressed anteriorly. Cardinal process lobes ponderous, with flat myophores; notothyrial platform low, very reduced.

Description.—Shell of large size (largest specimen 51.7 mm wide), lateral profile planoconvex to concavoconvex, semicircular in outline; maximum valve width at hinge line in young specimens and at mid valve length in adult ones; slightly acute cardinal angles in early growth stages and slightly obtuse in adult stages. Ventral valve 73–80% as long as wide (x = 76%; n = 3; σn = 0.02) and approximately 9% as deep as long, with slightly convex lateral profile. Ventral interarea planar, apsacline, 7% as long as valve length; delthyrium with apical pseudodeltidium. Dorsal valve almost flat to slightly concave, approximately 78% as long as wide; dorsal interarea anacline, 4% as long as valve length; notothyrium completely covered by a medially grooved, convex chilidium.

Radial ornament parvicostellate, with 6 ribs per 2 mm at 10 mm anteromedially from umbo, all of them with subquadrate crests, not clearly organized in sectors; ribs twice as wide as intercostal spaces. Concentric ornamentation consisting of fine fila, with counts of 5 per mm, intersecting radial ornament; some specimens show evidences of shell damage, reflected as discontinuities in shell ornament varying the density of ribs per millimetre and even forming irregular lamellae close to the shell margins ( Fig. 14C ).

Ventral interior with strong teeth, short dental plates extending forward approximately 10% of valve length and with average dental plates divergence angle of 99° (range 93–103°; n = 3); muscle field large, poorly impressed anteriorly, flabelliform and surrounded posterolaterally by very narrow and thin muscle bounding ridges. Adductor scars lanceolate located between diductor scars and approximately 15% as wide as muscle scar maximum width; myophragm well developed posteriorly to adductor scars.

Dorsal interior with thin and about 85° divergent socket ridges, bounding anteriorly triangular dental sockets; bifid cardinal process with ponderous lobes, weakly divergent anteriorly, with flat myophores. They are located on very reduced, low notothyrial platform, continuous anteriorly with broad and low median ridge halving the poorly impressed dorsal muscle field. Pseudopunctae visible in both interiors, excepting on muscle scars, with radial regular arrangement over the entire shell except for posterolateral portion where it displays a more irregular pattern and coarseness.

Remarks.—Although the low number of available specimens is insufficient to study the intraspecific variability of this species of Rafinesquina (Mesogeina) , the recorded material is appropriate to characterize its internal and external morphology and shows clear differences to the other Rafinesquina (Mesogeina) species described to date. Rafinesquina (Mesogeina) loredensis sp. nov. differs from the other Mediterranean species in having a more transversely elongate outline and ribs subquadrate in section, twice as wide as the intercostal spaces.

Young (1985) classified some rafinesquinid shells from Portugal as Hedstroemina mundae (Sharpe in Ribeiro et al., 1853). I propose to ascribe a part of that material to Rafinesquina (Mesogeina) pseudoloricata ( Barrande, 1848) see discussion under remarks of this species below). The rest of those Portuguese shells, with a clear transversally elongate outline ( Young 1985: pl. 34: 3, 8, 9), are included herein in the new species R. (Mesogeina) loredensis ( Fig. 14A, D, E ). The Portuguese species Orthis? mundae Sharpe in Ribeiro et al., 1853 only known from a single ventral valve, is possibly also a rafinesquinine. However, its rounded outline and the remarkable inequality of its parvicostellate ornamentation discriminates the latter species from R. (Mesogeina) loredensis sp. nov., which possesses semicircular outline and parvicostellae only loosely arranged in sectors.

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

Figures

Fig. 14. Rafinesquinine brachiopod Rafinesquina (Mesogeina) loredensis sp. nov.; middle Katian (Ka2), Upper Ordovician; Porto de Santa Anna Formation, Portuguese Central Iberian Zone, Portugal. A. IGM-2919, holotype, internal mould (A1), latex cast of interior (A2), detail of pseudopunctae (A3) of a ventral valve. B. IGM-2926, paratype, internal mould of dorsal valve (B1), details of cardinalia in posteroventral (B2) and anteroventral (B3) views. C. IGM-2925, paratype, latex cast of exterior of dorsal valve. D. IGM-2927, paratype, internal mould of ventral valve. E. IGM-2923, paratype, internal mould of small ventral valve. Scale bars 2 mm.