Amphibian
Amphibians lay their eggs in water, usually in a foam nest. After hatching they are tadpoles, which live in the water and have gills. The tadpoles change into adults in a process called metamorphosis.  When they are adult, they have lungs to breathe instead of gills, and legs. Adult amphibians also use their skin to take in oxygen, and some species of salamanders do not have lungs.