The Testudines are the only shelled species of reptile or amphibians. All Turtles and Tortoises have a carapace (upper shell) and a plastron (lower shell) to some degree. Sea turtles have a very aerodynamic shell which is thoroughly connected while tortoises have large, dome-shaped shells which look quite cumbersome.
There are two main groupings of turtles. The Pleurodira and the Cryptodira. The Pleurodira include the Chelus and Pelomedusa species and retract their heads by bending their necks horizontally. Conversely, the Cryptodira, which comprise most of the Testudines, retract their heads by bending their necks vertically.
Order Testudines (Turtles)
Family Chelydridae (Snapping Turtles)
(Pond Turtles / Box
and Water Turtles)
Family Testudinidae (Tortoises)
Family Dermatemydidae (River Turtles)
Family Kinosternidae (Mud and Musk Turtles)
Family Carettochelyidae (Pig Nosed Turtles)
Family Pelomedusidae (Afro-American Sideneck Turtles)
Family Chelidae (Austro-American Sideneck Turtles)