The Cryptodira are a suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira in that they lower their necks and pull the heads straight back into the shells, instead of folding their necks sideways along the body under the shells' marginals. They include among their species freshwater turtles, snapping turtles, tortoises, softshell turtles, and sea turtles.
Cryptodira
Skull of a cryptodiran turtle from the family Emydidae
Dorsal view of skull and cervical vertebrae of a cryptodiran turtle from the family Emydidae. Not all cervical vertebrae are featured due to the dissection cut.
Manchurochelys liaoxiensis was a member of Sinemydidae.
Turtles, or testudines, are reptiles of the order Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira and Cryptodira, which differ in the way the head retracts. There are 360 living and recently extinct species of turtles, 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. Like other amniotes they breathe air and do not lay eggs underwater, although many species live in or around water.
Turtle
Head and neck of a European pond turtle
Sea turtles have streamlined shells and limbs adapted for fast and efficient swimming.
The red-eared slider has an exceptional seven types of color-detecting cells in its eyes.