Green turtle (Laszlo Ilyes / CC BY)
See turtles (Testudines) are marine reptiles. All sea turtles breathe air. However, after changing to an anaerobic metabolism, they can stay underwater for long periods of time. There are 7 species of sea turtles: green sea turtle, loggerhead sea turtle, leatherback sea turtle, hawksbill sea turtle, Kemp's ridley sea turtle, flatback sea turtle, and olive ridley sea turtle. The largest species (leatherback sea turtle) can grow up to 2.1 meters (7 feet) in length. According to the IUCN Red List of Threatened Species, sea turtles are classified as threatened.