A few species, including box turtles and wood turtles, dwell mainly on land. There are at least seven species of sea turtles. Most zoologists classify these species into one family. The seventh species, the leatherback, forms its own family. Its shell has far fewer bones than that of the other sea turtles and is covered with skin rather than scutes.
Most sea turtles live in warm seas throughout the world.
The leatherback often ventures into cold Canadian waters. All except the Australian flatback may be found in the coastal waters of the United States. Sea turtles rank among the largest species. Sea turtles swim by beating their flippers much as a bird flaps its wings. Sea turtles cannot withdraw into their shell, and so they depend on their size and swimming speed for defense.