A planula's the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species. In all cases, the planula forms directly from the fertilized egg of a medusa, as the case in scyphozoans and some hydrozoans, or from a polyp, as in the case of anthozoans. Depending on the species, the planula either metamorphoses directly into a free-swimming, miniature version of the adult form (such as many open-ocean scyphozoans), or navigates through the water until it reach… (More on Planula)