Tortoises (/ˈtɔːr.təs.ɪz/) are reptiles of the family Testudinidae of the order Testudines (Latin: tortoise). Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like other members of the suborder Cryptodira, they retract their necks and heads directly backward into the shell to protect them. Tortoises are placid and slow-moving, with an average walking speed of 0.2–0.5 km/h.