Metamorphosis is a procedure in biology by which an individual physically expands after birth or hatching, that involves important change in form as well as growth and separation. It usually accompanies a change of habitat or of habits, but may occur without such change. Insects, amphibians and some additional organisms undergo metamorphosis.
Change of habits or habitat
Many insects and amphibians undertake metamorphosis with a important change in habits and habitat. undeveloped dragonflies are aquatic, though the adults are flying insects, and frogs undergo a metamorphosis from an water tadpole to an amphibious adult form. Change of habits is illustrated by the renovation of the free-swimming young of many water invertebrates into sessile adults (eg sea squirts), and the development of butterflies and moths from caterpillars with crushing mouthparts into flying insects with sucking mouthparts.
By compare, many crustacean genus undergo significant physical metamorphosis without altering habits or habitat significantly.
It was once thinking that, in cases where the animal's habitat remains unchanged, metamorphosis tracked a series of forms representing evolutionary ancestors of the species in question (see ontogeny recapitulates phylogeny), but this is no longer thought to be factual.