urtles do not have exoskeletons, because the muscles of an animal with an exoskeleton are located inside of the bones. That is clearly not the case with turtles. The shell of a turtle is part of the endoskeleton that is exposed to the outside, but then so is the horn of a cow or a goat. The cow's horn is bone covered by a layer of keratin. The turtle shell is also bone covered by scutes, which are made of keratin. Animals with exoskeletons, such as insects and crabs, must discard their old skeleton as they grow, in a process called molting. A new skeleton forms under the old, discarded old skeleton. Animals with endoseletons simply add additional layers to the old skeleton as they grow. They never discard their old skeletons and just keep the ones they got from birth.