by either passive or active means. The eggs of some digeneans, for example, are (passively) eaten by snails (or, rarely, by an annelid worm), in which they proceed to hatch. Alternatively, eggs may hatch in water to release an actively swimming, ciliated larva, the miracidium, which must locate and penetrate the body wall of the snail host.

After post-ingestion hatching or penetration of the snail, the miracidium metamorphoses into a simple, sac-like mother sporocyst.