Most scientists recognize eight species of these marine reptiles. Experts can identify each by the number and pattern of scutes (horny plates) on the carapace (top shell). Sea turtle species range in length from about 53 cm (21 in.) up to 1.9 m (6 ft.). Males and females are about the same size.

Sea turtles are found in tropical and temperate seas throughout the world. Adults of most species inhabit shallow coastal waters. Some species migrate great distances form winter feeding grounds to summer nesting areas.

Sea turtles' long, paddlelike flippers are adapted to locomotion in the water. Sea turtles are strong swimmers and divers. Green sea turtles can stay under water as long as five hours. To conserve oxygen, their hearts can slow to one beat every nine minutes.

Diets vary greatly among sea turtle species. Green and black sea turtles feed on seagrasses and algae. Loggerheads' and ridleys' strong jaws can crush crabs, shrimps, and molluscs. Leatherbacks prey only on jellyfish and other soft-bodied animals.

In general, sea turtles do not come out onto land, except females when they nest. Most nest during the warmest months, returning to the same beaches year after year. A female turtle digs a pit in the sand using her hind flippers, and deposits 50 to 200 eggs the size of ping pong balls. The incubation period for most species is 45 to 70 days.

All eight sea turtle species are listed as either endangered or threatened. Despite several management measures to preserve sea turtles, their future is still in question, due to a number of natural and human-induced factors.