The germinal vesicle of the mature egg probably breaks down either before or immediately after it is released. The fertilization membrane is not well marked. They remain attached to the egg. Cleavage is unequal and spiral. The yolk lobe is very prominent and a marked trefoil stage is present during first cleavage.
Gastrulation is by epiboly followed by invagination.
The ciliated gastrula rotates through the water. It is propelled through the water, rotating about its longitudinal axis. The shell appears about 14 hours after insemination, and grows rapidly, forming a straight hinge in the young veliger. The larva is propelled through the water by a conspicuous ciliated velum. Gill filaments and the posterior adductor muscle are present, and the mantle has now become conspicuous.