When first shed, the egg is irregular, hexagonal or pear-shaped, but on exposure to sea water it quickly becomes spherical, measuring 45 to 54 microns in diameter. It is somewhat opaque. The ovum is shed in the germinal vesicle stage. The germinal vesicle breaks down shortly after insemination and two polar bodies are quickly formed by two maturation divisions. A thin fertilization membrane is present.
Cleavage is unequal and spiral, with large polar lobes forming during the first two divisions.
The time is calculated from insemination. Metamorphosis A rounded trochophore is formed, with an aboral circle of cilia. It rapidly develops into a veliger by the expansion of the prototroch into a round, flat velum and by formation of a shell, bivalved from the time of its origin. The straight-hinge larva is a delicate pink in color. This color darkens to reddish-brown in the older veliger, which has a prominent foot, digestive tract and gills before metamorphosis.