Turtles are reptiles characterized by a shell developed mainly from their ribs. The shell consists of two parts: the domed carapace on the back, and the flatter plastron on the belly. There are 360 living and recently extinct turtle species, including land-dwelling tortoises and freshwater terrapins. They are found on most continents, some islands and, in the case of sea turtles, much of the ocean. Their closest living relatives are crocodilians and birds. Turtles are ectotherms or "cold-blooded", meaning that their internal temperature varies with their direct environment. They are generally opportunistic omnivores and mainly feed with limited movements. Turtles lay their eggs on land; sea turtles migrate long distances to lay their eggs on a favored beach. Turtles have appeared in myths and folktales. Some species are widely kept as pets. Turtles have been hunted for their meat and shells, and for use in traditional medicine. Many species are threatened due to habitat destruction. (Full article...)