Larva

A larva (Latin; plural larvae) is a young (juvenile) form of animal with indirect development, going through or undergoing metamorphosis (for example, insects, amphibians, or cnidarians).

The larva can look completely different from the adult form, for example, a caterpillar differs from a butterfly. Larvae often have special (larval) organs which do not occur in the adult form. 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.
Eurosta solidaginis Goldenrod Gall Fly larva

It is a misunderstanding that the larval form always reflects the group's evolutionary history. It could be the case, but often the larval stage has evolved secondarily, as in insects. In these cases the larval form might differ more from the group's common origin than the adult form.

The early life stages of most fish species are considerably different from juveniles and adults of their species and are called larvae.

Names of various kinds of larvae:
Insects (Class Insecta) are the biggest class of arthropods and the only ones with wings. They are the most diverse group of animals on the Earth, where they're most diverse at the equator and their diversity declines toward the poles. With over a million described species—more than half of all known living organisms[2][3]—with estimates of undescribed species as high as 30 million, thus potentially representing over 90% of the differing life forms on the planet.[4] Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, the crustaceans.

There are approximately 2,000 praying mantis, 5,000 dragonfly species, 20,000 grasshopper, 82,000 true bug, 120,000 fly, 110,000 bee, wasp ant and sawfly, 170,000 butterfly and moth, and 360,000 beetle species described to date. Estimates of the total number of current species, including those not yet known to science, range from two million to fifty million, with newer studies favouring a lower figure of about six to ten million.[2][5][6] Adult modern insects range in size from a 0.139 mm (0.00547 in) fairyfly (Dicopomorpha echmepterygis) to a 56.7 centimetres (22.3 in) long stick insect (Phobaeticus chani).[7] The heaviest documented insect was a Giant Weta of 70 g (2½ oz), but other possible candidates include the Goliath beetles Goliathus goliatus, Goliathus regius and Cerambycid beetles such as Titanus giganteus, though no one is certain which is truly the heaviest.[8]

The study of insects (from Latin insectus, meaning "cut into sections") is called entomology, from the Greek εντομον, also meaning "cut into sections".[9]