Salt water Crocodile
Do you know that crocodiles have a super immune system that very rarely do they catch a disease?
See all the crocodile pictures in this stream.
Though crocs breathe like land animals and not like fish, they can remain under water for hours. They bring down their metabolic rate so much that their oxygen requirement is minimal. The picture shows the toungue which folds back to cover the throat.
Crocs use their teeth more to hold their prey as they swallow food whole. Their jaws are very powerful exerting incredible amount of power as they close. However, curiously, the muscles controlling the jaws to open are so weak that held tight by a human they can't open the jaws.