In past times its intraspecific variability was the reason for variety species of no taxonomic value set up by several authors. Juvenile forms have got a really different outline compared with the adult specimens. Indeed anteriorly they have a very accentuated dorsal concavity near umbo and a more stretched form than the adult specimens which have a more or less const, roundish, lenticular outline. There exist also forms without the typical anterior-umbonal concavity and careened expansion (lenticularis form).

Habitat: this species lives in littoral area on sandy bottom. Also found into brackish water (Ganzirri lake, Messina - Italy, Spada 1969). Distribution: very common all over the Mediterranean and the Black Sea too.