Purpurocardia elegantoides ( Ortmann, 1899 )

Pérez, Damián E. & Del Río, Claudia J., 2017, Systematics of the family Carditidae (Bivalvia: Archiheterodonta) in the Cenozoic of Argentina, Zootaxa 4338 (1), pp. 51-84 : 72-73

Purpurocardia elegantoides ( Ortmann, 1899)

Figure 6.1–5

v* 1899 Cardita elegantoides Ortmann , p. 428.

1902 Cardita elegantoides Ortmann—Ortmann , p. 125–126, pl. 26, figs. 5a–c..1907 Venericardia sylva Ihering , p. 346–347, pl. 24, figs. 98a–b. v2000 Venericardia elegantoides (Ortmann) —Camacho et al., p. 68–69, figs. 3m –o. 2012 Cardita elegantoides Ortmann—Ojeda , p. 125.

Type specimen. Holotype PRI.66394, right valve from Punta Arenas (Tierra del Fuego Province, Loreto Formation, Chile).

Other material. PRI.66395; CIRGEO-PI 2276; MLP 26811 (8 left valves and 11 right valves).

Diagnosis. Shell small-sized (less than 30 mm in length) with subrectangular outline. Posterior area defined by six to seven radial ribs narrower than the remainder. Umbo large. Lunule very convex. Right valve hinge with slightly defined sinuous ventral edge. Left anterior tooth slightly inclined posteriorly. External sculpture of 22 to 23 radial ribs, paracostal ribs very reduced, intercostal spaces with ‘U’-shaped transversal section.

Description. Shell small-sized with subrectangular outline in anterior-posterior direction; dorsal margin straight and gently sloping, posterior margin slightly truncated, ventral and anterior margins smooth and rounded. Umbo large, rounded, placed near anterior third of the valve length. Lunule small, very convex, prominent and weakly separated by a groove from remaining surface of shell.

Right valve hinge with a slightly sinuous ventral edge; small, triangular, narrow, short and straight anterior tooth; middle tooth very broad, inclined posteriorly, with broad base, ventrally concave with flat anterior and gentle convex posterior sides, and higher towards apex on lateral view; posterior tooth narrow and straight. Left valve hinge with a straight ventral edge; anterior tooth strong, broad, triangular, slightly inclined posteriorly; posterior tooth elongate, narrow and curved.

External sculpture of 22 to 23 tripartite radial ribs, short, wide, with subelliptic transverse section; covered with very low nodes of subrectangular transverse section; very reduced paracostal ribs; wide intercostal spaces with ‘U’-shaped transverse section. Pallial line one-fifth of total valve height. Inner ventral margin strongly crenulated; crenulations subtriangular, truncated, covering entire margin to upper tip of posterior adductor muscle scar.

Remarks. Ortmann (1899) introduced Cardita elegantoides based on six shells collected by J. Hatcher in Punta Arenas (Eocene, Loreto Formation, Chile). Later, Ortmann (1902) mentioned this species from Monte Observación and mouth of Santa Cruz River (lower Miocene, Monte León Formation, Santa Cruz Province). As stated above, Ihering (1907) proposed a new name for the specimens from Tierra del Fuego but including the holotype of C. elegantoides . Therefore, this new name is a junior synonym of C. elegantoides . Recently, Ojeda (2012) revised Hatcher’s fossil localities and assigned an upper Eocene age to the Loreto Formation with ( Otero et al. 2012).

Purpurocardia elegantoides is placed in Purpurocardia by its subrectangular outline, slightly truncated posterior margin, small lunule, right valve hinge with a slightly sinuous ventral edge, triangular, broad and ventrally concave right middle tooth, short and triangular left anterior tooth and 22 to 23 wide radial ribs with very reduced paracostal ribs.

Purpurocardia elegantoides can be distinguished from P. purpurata ( Deshayes, 1854) ( Beu 2006: pl. 18, figs. B, D, E) by having a strongly defined posterior area, larger umbo, more convex lunule, less pronounced sinuosity of right hinge ventral edge, slightly inclined posteriorly instead vertical left anterior tooth and low number of radial ribs.

Purpurocardia elegantoides differs from P. perscrupulosa ( Marwick, 1932) ( Beu & Maxwell 1990: pl. 17, figs. d, e) (lower–middle Miocene, New Zealand) by having a smaller shell, a more convex lunule, slightly inclined posteriorly left anterior tooth, lower number of radial ribs and more reduced paracostal ribs.

Purpurocardia elegantoides can be separated from P. beata ( Marwick, 1928: figs. 48 and 50) (upper Miocene– upper Pliocene, New Zealand) and P. titirangiensis ( Marwick, 1943) (= Venericardia martini Marwick, 1928 : figs. 52–53) (upper Pliocene–lower Pleistocene, New Zealand) by its smaller shell, subrectangular outline in anteriorposterior direction, lower number of radial ribs and intercostal spaces with ‘U’-shaped transverse section.

Purpurocardia elegantoides differs from P. urutiensis ( Marwick, 1926: pl. 75, figs. 1 and 3) (upper Miocene, New Zealand) by a posterior area with narrower radial ribs, more convex lunule, left anterior tooth inclined posteriorly instead of vertically and wider intercostal spaces.