Due to pressure within the ovary, the newly-shed egg is often irregular in shape, and one axis may be longer than the other. The ovum is very yolky and appears white and opaque. It is shed in metaphase of the first maturation division. A fertilization membrane is formed, cleavage is spiral and unequal. Poorly defined polar lobes are developed.
Gastrulation is by epiboly, followed by invagination.
Time is calculated from insemination. A mouth and shell gland are formed. The shell of the early veliger is bivalved and has a straight hinge line. Two adductor muscles are present. The mouth, stomach and small intestine are clearly visible, but the mantle is inconspicuous.