Sea turtles (Superfamily Chelonioidea) are turtles found in all the world's oceans except the Arctic Ocean .There are seven living species of sea turtles: flatback, green, hawksbill, Kemp's Ridley, leatherback, loggerhead and olive ridley. Although they have been around for tens of millions of years since the Mesozoic, the body plan of sea turtles has remained relatively constant.