larva

A larva  is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. Larva is Latin for "ghost."
The larva's appearance is generally very different from the adult form (e.g. caterpillars and butterflies), and a larva often has unique structures and larval organs that do not occur in the adult form. A larva's diet can be considerably different from its adult form.
Larvae are frequently adapted to environments separate from adults. For example, some larvae such as tadpoles live exclusively in aquatic environments, but as adults can live outside water as frogs. By living in distinct environments, larvae may be given shelter from predators and reduce competition for resources with the adult population.
Animals in the larval stage will consume food to fuel their transition into the adult form. Some species such as barnacles are immobile as adults, and use their mobile larvae form to distribute themselves.
The larvae of some species can become pubescent and not further develop into the adult form (for example, in some newts). This is a type of neoteny.