The shell is probably one of the reasons that turtles and tortoises live as long as they do. Simply, it protects them from predators and bad weather. It’s made up of the carapace, which is on top, and the plastron, which is on the underside. Extensions on the plastron connect it to the carapace. Both the carapace and the plastron are made out of bone. Exceptions to this are softshell turtles and the leatherback turtle, which is a sea turtle. Some turtles, such as box turtles, can pull their head, legs, and tail into their shell, and shut it completely.
A person can sometimes tell the difference between a turtle and a tortoise by the shape of the shell. Tortoises tend to have domed shells while the shells of turtles are flatter. The shells of sea turtles are flat and smooth to make them more hydrodynamic.