Akardita iberica, Perna & Brunetti & Bella, 2018

Perna, Rafael La, Brunetti, Mauro M. & Bella, Giano Della, 2018, Systematic position of two Pliocene carditids with description of Akardita n. gen. and A. iberica n. sp. (Bivalvia: Carditidae), Zootaxa 4379 (2), pp. 215-230 : 222-223

Akardita iberica n. sp.

Fig. 5A – K

Type material. Holotype, two paired valves (MZB 47004); paratype 1, RV (MZB 47005); paratype 2, RV (MZB 47005).

Type locality. Lucena del Puerto, province of Huelva, Andalusia, southern Spain.

Stratum typicum. Yellowish fine sands with intercalating shell beds, Arenas de Huelva Formation, lower Pliocene (Zanclean).

Etymology. The species is named after the geographic origin of the type material from the Iberian Peninsula.

Other material. 1 valve, Lucena del Puerto, lower Pliocene (Della Bella coll. GDB/092); 5 valves, Lucena del Puerto, lower Pliocene (Brunetti coll. S297LDP).

Diagnosis. A large species of Akardita n. gen., exceeding 40 mm in length, notably robust, with 21–24 radial ribs.

Description. Shell large, up to ca. 45 mm in length, robust, equivalve, moderately inflated. Shape slightly elongate, ovate-subquadrate, moderately inequilateral, well rounded anteriorly, moderately convex ventrally, weakly truncate posteriorly. Umbo relatively small, poorly sticking out from outline, prosogyrate. Lunule small, slightly concave; escutcheon markedly elongate, deeply sunken. Ligament external, elongate, opisthodetic.

Radial sculpture consisting of 21 poorly convex ribs. Radial interspaces, narrow, shallow, poorly impressed ventrally. Commarginal sculpture of closely set growth striae, producing a poorly distinct, somewhat irregular decussate pattern, ventrally replaced by coarse, lamellose sculpture. Posterior slope distinct, with 5 notably finer radial ribs. Early stage sculpture consisting of beaded radial ribs, with deeper and slightly larger interspaces than in adult stage.

Hinge plate moderately robust, slightly arched. Right hinge with three cardinal teeth: anterior tooth small, poorly developed; central tooth robust, triangular-elongate, strongly oblique; posterior tooth elongate, parallel to posterior-dorsal margin. Left hinge with two cardinal teeth: anterior tooth smaller, subtrigonal, slightly oblique; posterior tooth larger, elongate, parallel to posterior-dorsal margin. Lateral dentition represented, on both valves, by a small, tubercle-shaped anterior lateral tooth, and by a shallow, elongate, barely seen posterior thickening, close to hinge plate ending.

Inner margin coarsely crenulated anteriorly and ventrally, posteriorly almost smooth. Pallial line entire, moderately convex. Anterior adductor muscle scar slightly larger, reniform; posterior scar roughly triangular; both well distinct.

Measurements. Holotype, L 42.5 mm, H 37.1 mm, W 13.7 mm; paratype 1, L 42.6 mm, H 38.6 mm, W 15.4 mm; paratype 2, L ~ 40 mm (estimated), H 39.5 mm, W 13.1 mm. Other material up to L 45.9 mm.

Distribution. The species is only known from the type locality.

Remarks. The available material shows a moderate variability in rib number, ranging from 21 to 24. The new species differs from A. subrevoluta by being much larger (up to ca. 45 mm in length, while A. subrevoluta does not exceed 25 mm), markedly more robust, slightly more inequilateral, ventrally more convex, umbo less prominent, and rib number with a limited overlap at 24 ribs.

The new species resembles the undescribed species from the Pliocene of Portugal, here referred to as Cardita matheroni sensu Dollfus & Cotter, 1909 . According to illustrations by Dollfus & Cotter (1909: pl. 4, figs 21 – 26), the species from Portugal has poorly convex ribs without nodulose sculpture. It differs from Akardita iberica n. sp. by being more rounded in outline and by the occurrence of some particularly deep, irregularly spaced growth striae, in addition to the finer ones. Both species are similar in size, exceeding 40 mm in length.

The original Cardita matheroni Mayer, 1871 , is from the upper Miocene Congeria beds in the area of Bollène, southern France ( Mayer 1871). According to Mayer, his species is similar to Cardites antiquatus and to Cardita partschi Goldfuss, 1840 . The Miocene C. partschi is in turn similar to C. antiquatus , with nodulose ribs ( Sieber 1956; Schultz 2003; Caze et al. 2010). Cardita matheroni sensu Fontannes, 1882 , from the Pliocene of the Rhone Valley ( Fontannes 1882: 122, pl. 7, fig 15 – 17) seems to be yet another distinct species.

Figures

FIGURE 5. Akardita iberica n. sp., Lucena del Puerto (Huelva), Spain, lower Pliocene. A–D, G, H, J, K. Holotype (MZB 47004).E, F. Paratype1, RV (MZB 47005).I. Paratype 2,RV (MZB 47005).Scalebars:20 mm (A–F), 10mm (G, H, K), 2 mm (I, J).