Tortoises () are reptile species of the family Testudinidae of the order Testudines (Latin: tortoise). They are particularly distinguished from other turtles (which includes the order Chelonia) by being exclusively land-dwelling, while many (though not all) other turtle species are at least partly aquatic. 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 backwards into the shell to protect them. Tortoises can vary in size with some species, such as the Galapagos giant tortoise, growing to more than 1. 2 m in length, whereas others like the Speckled cape tortoise have shells that measure only 68 cm long. Several lineages of tortoises have independently evolved very large body sizes in excess of 100 kg, including the Galapagos giant tortoise and the Aldabra giant tortoise. They are usually diurnal animals with tendencies to be crepuscular depending on the ambient temperatures. They are generally reclusive animals. Tortoises are the longest-living land animals in the world, although the longest-living species of tortoise is a matter of debate. Galpagos tortoises are noted to live over 150 years, but an Aldabra giant tortoise named Adwaita may have lived an estimated 255 years.