tadpole

The larva of an amphibian, especially a frog or toad; largest 25 cm/10 in long; usually a short spherical body, feathery gills, large tail; most eat microscopic plants; with age, gills and tail shrink, legs appear, and larvae become carnivorous; also known as pollywog, or porwiggle (from Old English tade poll, ‘toad head’, Middle English pollwyggle, ‘head wiggle’).

A tadpole (also known as a pollywog or polliwog) is a larval amphibian, the juvenile form of a frog, toad, newt, salamander, or caecilian.

In this stage it breathes by means of external or internal gills, is at first lacking legs, and has a fin-like tail with which it swims as most fish do, by lateral undulation. As a tadpole matures, it metamorphoses by gradually growing limbs and then (in the case of frogs and toads) absorbing its tail by apoptosis (controlled cell death). Tadpoles depend very much on clean water. Most tadpoles are herbivorous, subsisting on algae or other greens such as boiled lettuce in captivity. In a few species, some tadpoles turn cannibalistic under harsh conditions and feed on other tadpoles living in the pond. As a tadpole develops it grows two back legs and then front legs. The tadpole's gills disappear as its lungs develop. When the tadpole has fully transformed into a frog it can leave the water in search of a mate.