Development of larval shell of Macoma balthica (Bivalvia: Tellinidae) in the White Sea

The development of the larval shell and hinge of the bivalve mollusk Macoma balthica in the White Sea is described. Macoma spawning occurs at the end of June. Larvae at the D-stage of development have a shell length of 120-140 µm. The shell is oval, the hinge edge is straight with a noticeable striation. During development, the shell becomes more elongated with a pointed anterior end. A characteristic feature is the expressed concentric striation of prodissoconch II. The umbos are low and rounded. Hinge edge is straight, with small teeth of provinculum. The ligament occupies the central position. At later stages, a pair of large hook-shaped teeth is formed in the anterior part of the hinge. Metamorphosis occurs at shell length of 300-310 µm.