Tadpole

(Wikipedia) A tadpole or polliwog (also pollywog or porwigle) is the larval stage in the life cycle of an amphibian, particularly that of a frog or toad.Tadpoles are young amphibians that usually live in the water.During the tadpole stage of the amphibian life cycle, most respire by gills. They do not usually have arms or legs until the transition to adulthood, and typically have dorsal or fin-like appendages and a tail with which they swim by lateral undulation, similar to most fish.
As a tadpole it usually developed legs first then arms and then absorbing its tail by apoptosis. Lungs develop around the time of leg development, and tadpoles late in development will often be found near the surface of the water, where they breathe air. During the final stages of external metamorphosis, the tadpole's mouth changes from a small, enclosed mouth at the front of the head to a large mouth the same width as the head. The intestines shorten to make way for the new diet.