Twelve turtle facts that you should know before getting into the ocean or engaging in a turtle discussion with other divers... 1. The Kemp's ridley is the smallest sea turtle, the leatherback the largest. The largest leatherback ever recorded tipped the scales at 2,019 pounds.2. Sea turtles do not have external ears or ear openings but do have eardrums, middle- and inner-ear structures. They hear low-frequency sound best.3. A sea turtle cannot retract its head or limbs into its shell the way other turtle species can.4. Sea turtles can live almost indefinitely without freshwater thanks to a body function that extracts the salt from seawater. Glands in their eyes excrete the excess salt.5. Green turtles are so named because of the color of their body fat, not the color of their shell or skin.6. A sea turtle can smell quite well while submerged by taking water in through its nostrils and pushing it out through its mouth.7. Leatherbacks routinely dive to more than 1,000 feet and may reach depths beyond 3,900 feet in pursuit of a jellyfish dinner.8. Sea turtles have good vision underwater but are otherwise nearsighted.9. A green turtle's heart may beat only once every nine minutes to conserve oxygen during dives that can last as long as five hours.10. Turtles (land and sea) do not have teeth, but do have highly differentiated jaws that are suited for their diets.11. Commonly called the shell, a sea turtle's rigid exterior armor is actually an outer layer of horny plates called scutes that cover the true shell. (Leatherbacks are the only exception.) The top of the shell is called the carapace; the bottom is the plastron.12. Size does not indicate gender. The easiest way to tell boys from girls: males have larger, longer tails because their reproductive organs are housed in the base.