There are two species of alligator in the world: the Chinese alligator and the American alligator. Both species have movable tongues attached to the lower jaw. This is one feature that distinguishes an alligator from a crocodile, as a crocodile has an immovable tongue on the roof of its mouth.
Alligators can stick their tongues out, but crocodiles cannot because of the presence of a membrane in the roof of a crocodile's mouth that holds the tongue in place. Because crocodiles spend the majority of their time in the water, this membrane holding the tongue keeps water out of the airway and lungs. Alligators have a flap of skin called a palatal valve, located at the back of the throat, which allows the alligator to stick out its tongue and snap its jaws open and shut without inhaling water.