Conchological variability of Anadara kagoshimensis (Bivalvia: Arcidae) in the northern part of the Black–Azov Sea basin

Features of shape and size variability of blood ark (Anadara kagoshimensis) inhabiting biotopes in the northern part of the Black and Azov Seas were studied. Fourteen morphometric traits were measured for each blood ark shell. The principal component analysis extracted only one principal component (PC) whose eigenvalue is greater than 1.0. The PC 1 explained 84.5 % of the variation in morphometric traits and was interpreted to be an integral indicator of mollusk shell size. The variation of morphometric traits due to the size and asymmetry of the valves was subjected to correction using a Multiple General Linear Model with PC 1 as a continuous predictor and right or left valve as a discrete predictor. A cluster analysis was performed based on the residuals after size correction, as a result of which mollusk individuals were divided into four clusters. For mollusks from the Sea of Azov, a characteristic feature was an increased distance between pallial line and ventral shell margin. In turn, mollusks from the Black Sea exhibited an increase in the width of the posterior adductor scar. The observed morphological differences can be explained by different quantity and quality of food, since the soil composition in the biotopes studied is almost identical.