Procardium, Poorten & Perna, 2017
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https://doi.org/ 10.4202/app.00363.2017 |
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persistent identifier |
https://treatment.plazi.org/id/03F3E045-FFC0-575D-FF6D-56F0589EF0C1 |
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treatment provided by |
Felipe |
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scientific name |
Procardium |
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Genus Procardium View in CoL nov.
Etymology: From Latin, pro, before, early; and Cardium ; in reference to genus origin, putatively ancestral to Cardium (gender neuter).
Type species: Cardium indicum Lamarck, 1819 (= C. darwini May- er, 1866, C. delpeutum McGill, 1964 ), Recent, “Habite l’Ocean des grandes Indes” [Indian Ocean; erroneous, actually Western Africa].
Species included: Cardium diluvianum Lamarck, 1819 ; Cardium avisanense Fontannes, 1879 ; Cardium kunstleri Cossmann and Peyrot, 1912 ; Cardium danubianum Mayer, 1866 ; Procardium magnei sp. nov.; Procardium jansseni sp. nov.
Diagnosis. — Shell large, slightly longer than high, relatively thin and posteriorly gaping. 14–24 radial ribs, sculptured with horseshoe-shaped scales anteriorly and projecting spines posteriorly. Interspaces wider than ribs, often with a secondary riblet. Anterior cardinal blade like and posterior cardinal very small in left valve. Cardinal teeth erect, fully separated and similar in height in right valve.
Description.— Shell large (L 75–115 mm), generally slightly longer than high, weakly to strongly inequilateral, relatively thin, inflated, gaping posteriorly. Umbo orthogyrate to slightly prosogyrate. Anterior and ventral margins rounded, posterior margin truncated and nearly straight. Shell bearing 14–24 primary radial ribs, on anterior half each interspace with a weakly developed secondary riblet. Interspaces wider than primary ribs. Anterior ribs prominent with conical, ventrally hollow scales. Cross-section of anterior and median ribs roundly triangular or trapezium-shaped, sometimes with a radial groove on the rib tops. Ribs on postero-medial slope becoming asymmetrical in cross section, ultimately flattened posteriorly, with sculpture on posterior rib flanks gradually developing into pronounced, posteriorly directed spines. Rib impressions clearly visible from within, shell resorption present in rib impressions on postero-medial part. Hinge plate rather narrow and slightly sinuous, hinge angle very large (ca. 165–175°), cardinal teeth nearly horizontally rotated. Left valve: two cardinal teeth, the anterior one well defined and blade like, the posterior one tiny; both teeth connected at their bases and with a deep socket below. Right valve: two similar sized, erect, pointed cardinal teeth, not touching at their bases but separated by a deep socket. Anterior lateral sockets curved and extremely hollowed, lateral teeth of both valves thin, blade like. Tips of lateral teeth about equidistant from anterior cardinal. Ligament short. Lunule not well defined, dorsal margin slightly raised anterior of the umbo. Exterior colour dirty white, sometimes with commarginally arranged brownish areas, posteriorly pink or purple, except for white spines. Rusty-brown deposit present on interspaces of postero-medial part. Interior colour white with traces of cream, posterior margin purple.
Remarks.— Procardium gen. nov. can be separated from several related genera by a number of characters: the ribs are well developed, alternating with a tiny secondary riblet ( Fig. 1B, D, F View Fig ), anteriorly and medially carrying erect scales ( Fig. 1F View Fig ) and posteriorly strongly projecting spines. The shell is thin and gapes posteriorly ( Fig. 1E View Fig ). The hinge of the left valve has two very unequal cardinal teeth: the anterior one is elongate and blade like, located anterior to the very poorly developed posterior tooth. The right valve ( Fig. 1A View Fig ) has two projecting, equally sized and slightly diverging cardinals, that are fully separated and placed diagonally. It has an extremely excavated anterior lateral socket ( Fig. 2A View Fig ). The shell is white with a purple posterior slope.
In the related genus Cardium Linnaeus, 1758 , consisting of two Recent species, the type species Cardium costatum Linnaeus, 1758 and C. maxicostatum ter Poorten, 2007 , the ribs are very broad and flattened with a high projecting flange running on top, which is completely hollow. Additional rib sculpture is lacking, except for a poorly developed ridge running on the posterior ribs of C. maxicostatum . The shell is white, moderately solid and has a modest posterior gape. The interspaces never have a secondary riblet. The hinge of the left valve has two equally developed cardinal teeth, with the anterior tooth positioned ventral to the posterior tooth; the hinge of the right valve has two almost equal-sized projecting cardinals that are fully separated and placed along a horizontal axis. The hinge plate is straight ( Fig. 2B View Fig ).
A second related genus is Bucardium Gray, 1853 , with its type species and sole Recent representative Bucardium ringens (Bruguière, 1789) . A second species is known from the Burdigalian of the Aquitaine Basin, B. grateloupianum La Perna, 2016 . Bucardium has a rounded, solid, slightly gaping shell. The ribs are broad, with narrow interspaces, almost smooth, and the posterior ones are strongly protuberant, resulting in a deeply incised margin. The left valve has two very unequal cardinal teeth, with the anterior tooth positioned ventral to the posterior tooth; the cardinal teeth of the right valve are equally sized, rather short and largely fused ( Fig. 2C View Fig ). The shell is white with a pinkish-purple posterior slope. With a length of 50 mm (Recent) or 65 mm (fossil), Bucardium remains considerably smaller than the other two genera. Ringicardium Fischer, 1887 , mainly used in the literature for species now referred to Procardium gen. nov., is an objective synonym of Bucardium ( La Perna 2016) .
A third related species group, distinct from Procardium gen. nov., Cardium , and Bucardium , but of uncertain generic position, includes some species from the late Oligocene and early Miocene of Europe ( La Perna 2016). The best known of them is “ Cardium ” burdigalinum Lamarck, 1819 from the Burdigalian of the Aquitaine Basin ( La Perna 2016: figs. 6, 7). These species have thin, slightly gaping shells, 22–33 well developed radial ribs with rather narrow interspaces and attain a maximum size of about 75 mm. The anterior ribs carry elongate, flattish tubercles or small conical scales similar to those of Procardium gen. nov., and the posterior ribs are spiny and protuberant. The cardinal teeth in the right valve are largely fused with a deep socket below; the anterior lateral socket is not significantly excavated and the narrow hinge plate is moderately curved. In the right valve, the anterior and posterior ventral lateral teeth are approximately equidistant from the cardinals ( Fig. 2D View Fig ). Based on shell characters, these species seem to be significantly closer to Procardium gen. nov. than to other cardiids, but we regard them as representatives of a separate genus.
Acanthocardia Gray, 1851 View in CoL is a more distantly related European genus, with hardly or non-gaping shells, partly connected cardinal teeth in the left valve, a thicker shell and lacking a secondary riblet in the interspaces, in addition to other notable differences ( La Perna and D’Abramo 2009, 2013).
An overview of the discriminating shell characters of Cardium View in CoL , Bucardium View in CoL , and Procardium View in CoL gen. nov. is given in Table 1, while differences in the hinge regions between the three genera and “ C. ” burdigalinum View in CoL are shown in Fig. 2 View Fig .
Stratigraphic and geographic range.— Early Burdigalian or Aquitanian (early Miocene) to Recent. Miocene: Proto-Mediterranean, Western and Central Paratethys, NE Atlantic (Franco-Iberian coast to North Sea Basin); Plio-Pleistocene: southern Spain and Mediterranean; Recent: extreme southwestern Mediterranean and W Africa.
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