Cnidaria - Protozoa

The mature medusoid jellyfishes like Aurelia are the sexual stages. Sperms and eggs produced in the dissimilar (male and female) individuals ale released in water, which then fuse to form a zygote. The latter develops into a fixed polyploids scyphistoma that undergoes various transverse fission to produce ephyras by the process called Strobilation (see page lo), a type of asexual reproduction. Thus the sexual generation of the adult jellyfish is alternated along with an asexual generation i.e., scyphistoma. You would recall the alternation of generation is quite common among hydrozoans, in which the highly branching sedentary colonies such as those of Obelia are asexual generations. They give off medusae which are sexual generations. The medusae give rise to the colonies and vice versa, alternating with one another.