Morphometric and systematic study on three Acanthocardia species from the Mediterranean Pleistocene (Mollusca, Bivalvia, Cardiidae)

The cardiids Acanthocardia echinata (Linnaeus, 1758), A. deshayesii (Payraudeau, 1826) and A. lunulata (Seguenza, 1879) co-occur in the Mediterranean Pleistocene and are closely similar to each other, even partially overlapping in shell morphology. Of these, only A. echinata is fairly well known. Acanthocardia deshayesii has been considered a subspecies or even a synonym of A. echinata, whereas A. lunulata, only known from the original description, has been confused with A. deshayesii. The univariate and multivariate morphometric analysis on six shell characters substantiates the distinct taxonomic status of the three species. Acanthocardia mucronata (Poli, 1791), Cardium duregnei Monterosato, 1891 and C. bullatum Locard, 1892 are considered synonyms of A. echinata. Cardium propexum Monterosato, 1891 is proved to be a synonym of A. lunulata, an extinct species probably endemic to the Mediterranean, like A. deshayesii.