Sea turtles (Chelonioidea) are turtles found in all the world’s oceans except the Arctic Ocean, and some species travel between oceans. The term is US English. In British English they are simply called “turtles”; fresh-water chelonians are called “terrapins” and land chelonians are called tortoises.
There are seven types of sea turtles: Kemp’s Ridley, Flatback, Green, Olive Ridley, Loggerhead, Hawksbill and the leatherback. All but the leatherback are in the family Chelonioidea. The leatherback belongs to the family Dermochelyidae and is its only member. The leatherback sea turtle is the largest, measuring six or seven feet (2 m) in length at maturity, and three to five feet (1 to 1.5 m) in width, weighing up to 1300 pounds (600 kg). Most other species are smaller, being two to four feet in length (0.5 to 1 m) and proportionally less wide. The Flatback turtle is found solely on the northern coast of Australia.