The quadrupeds include almost all the mammals. (Among the exceptions are whales, bats, and humans.) The Greek equivalent of this Latin word is tetrapod. However, the two are not identical, since the tetrapod classification includes bipeds such as birds, in which two of the limbs are no longer used for walking. Insects all have six legs, of course, and in the sea there are eight-legged octopods (including the octopus). But there are no animals of any kind with an odd number of legs.