Metamorphosis, or a change in form, in biology means the transition from a larval stage to an adult stage. In most animals, embryonic development leads to the formation of a larval stage with very different characteristics than the adult stage. Larval morphology, or form, may be specialized for some function such as growth (which requires feeding and associated structures) or dispersal. Some larval forms, called exotrophic, feed, while others, called endotrophic, are nonfeeding. Juvenile and adult forms often live in very different environments.

Cnidarians have varying types of metamorphosis. Some species have three distinct life history stages: the planula, medusa, and polyp. The planula stage is the free-living larval stage. The medusa stage involves a single individual or a colony of individuals that act as a single free-swimming organism (examples include jellyfish and man-o-war). The polyp stage is sessile (adhered to the substrate) and may involve a single...