Noun
In embryonic development, a vesicle filled with fluid, formed from the morula by the divergence of its cells in such a manner as to give rise to a central space, around which the cells arrange themselves as an envelope; an embryonic form intermediate between the morula and gastrula. Sometimes used as synonymous with gastrula.
The very young, free-swimming larva of the coelenterates. It usually has a flattened oval or oblong form, and is entirely covered with cilia.
Source: Webster's dictionaryA few omit the planula, polyp and ephyra phases and produce new medusae directly from eggs. Source: Internet
After fertilization, the corals release planula that are ready to settle. Source: Internet
In moon jellies, the eggs lodge in pits on the oral arms, which form a temporary brood chamber for the developing planula larvae. Source: Internet