Metamorphosis

Metamorphosis is a biological process in which an animal undergoes a conspicuous and relatively abrupt change in its body structure as part of its development. Some insects, fish, amphibians, mollusks, crustaceans, cnidarians, echinoderms, and tunicates undergo metamorphosis, often accompanied by a change of nutrition or behavior. Some animal species undergo complete metamorphosis ("holometaboly")... (Wikipedia)