Turtle Turtle is the only reptile with a shell. Most kinds of turtles can pull their head, legs, and tail into their shell, which serves as a suit of armor. Few other backboned animals have such excellent natural protection. Turtles cannot be warm and active in cold weather, and so they cannot live in regions that are cold throughout the year. There are about 250 species of turtles, about 50 of which live in North America north of Mexico.
Some turtles live only on land, but others spend almost their entire life in the sea.
Most other species dwell mainly in fresh water or live about equally on land and in fresh water. Many turtles live their entire life within a few miles or kilometers of where they were hatched. But large numbers of sea turtles migrate thousands of miles or kilometers from their birthplace. Turtles vary greatly in size. Sea turtles, all of which swim rapidly, rank as the fastest turtles.