PDFDOI: https://doi.org/10.2478/vzoo-2014-0054
An alien species in the Black Sea and the Sea of Azov — Anadara inaequivalvis (Bruguiere, 1789) — was recently discovered to have a wide range of shell variability. From the investigated samples (over 900 valves) six basic types of the shell commissural opening were defi ned; they are not, however, discrete conditions. The presence of intermediate variants reveals a gradual (continuous) character of the shell variability and indicates that all the samples investigated belong to the same species. The variation of some other Anadara characteristics is also discussed, including: quantity and ornamentation of the ribs on the surface of the valves, quantity of chevrons on the ligament area, shape of the hinge plate and quantity of hinge teeth. A comparison of conchological characteristics of Anadara from the Black–Azov Sea Basin with A. inaequivalvis from southeast India shows that ranges and patterns of shell variability of Azov-Black Sea Anadara correspond to variability of A. inaequivalvis from this species type locality — Coromandel Coast of India.