Shell form, growth and life span of Astarte arctica and A. borealis (Mollusca: Bivalvia) from the subtidal zone of northeastern Sakhalin

This study investigates changes in body proportions during ontogenesis of the bivalves Astarte arctica and A. borealis from the subtidal zone of northeastern Sakhalin. Marked differences in the shell form of bivalves were found. The shell of A. arctica is convex and compact, shell length and height are comparable, and shell width is more than 50% of shell height. A. borealis has a slightly elongate and flattened shell, its width is less than 50% of its height. Shell proportions can provide a reliable criterion for differentiating the species. Mollusks grow at nearly the same rate but attain different maximum sizes. Linear growth is described by Bertalanffy’s equation: L t = 48.2[1 − e −0.4850(t − 0.4396) ] for A. arctica and L t = 53.1[1 − e −0.4106(t − 0.4253) ] for A. borealis . In northeastern Sakhalin, the life span of A. arctica is 7 years and of A. borealis , 8 years. By life span, the two bivalve species from Sakhalin slightly differ from their counterparts in other regions, particularly the arctic seas.