The Bornean Flat-headed Frog (Barbourula kalimantanensis) is a species of toad in the Bombinatoridae family. It is the second frog known to have no lungs.
Djoko Iskandar, an Indonesian zoologist, first described the Bornean Flat-headed Frog. However, he did not know the frog was lungless until other researchers cut eight of the specimens open in the lab. The frog breathes entirely through its skin, and its internal organs (the stomach, spleen and the liver) take up the space which normally would be filled by the lungs. By retaining the lunglessness of their tadpole stage, the frogs are much flatter than typical frogs, which might help absorb oxygen and avoid being swept away in fast streams.
[Excerpted from Wikipedia]