Turtles, tortoises and terrapins are all members of the order Testudines. These reptiles all have a protective shell that has developed from their ribs. The top half of a turtle’s shell is called the carapace and the underside portion is called the plastron.
Contrary to cartoons and children’s media, turtles cannot leave their shells.
There are an estimated 300 species of Testudines. Typically, the term “turtle” is used to describe species that are associated with fresh or salt water. “Tortoise” is used for species that are strictly confined to the land. The term “terrapin” is used for only one species, the Diamondback Terrapin, which is associated with brackish water.