Cnidaria and Platyhelminthes - Larval forms

Cnidaria

The common larval stage that is found in cnidarians is the planula which forms following gastrulation. The planula is elongated and radially symmetrical along with anterior and posterior ends. The surface is covered by ciliated cells. A mouth may be present, sometimes at the posterior end of the larva and the larva attaches by its anterior end. The planula might settle down to form a polyploids scyphistoma that ultimately farms the medusa. In several hydrozoans the planula forms the actinula larva that transforms into the medusa.

Platyhelminthes

Development in parasitic platyhelminths is usually complicated with several free swimming to parasitic larval forms. The progression is from miracidium to sporocyst to redia and cercaria.