A reptile (order Testudines) in which the body is enclosed by a shell of bony plates that form an upper carapace linked to a lower plastron. Some species are able to retract the head into the shell. The jaws are horny and lack teeth. The legs are strong, amphibious species having webbed digits. Diet varies depending on the habitat. There are 260 terrestrial, marine, and freshwater species found worldwide in tropical and temperate regions.