Cryptodira is a suborder of turtles that includes most of the world's turtle species. These turtles are characterized by their ability to retract their heads into their shells, which provides them with protection from predators. They are found in various habitats, including freshwater, marine, and terrestrial environments. The suborder is divided into two main groups: Pleurodira, which includes side-necked turtles, and Cryptodira, which features the more common hidden-necked turtles. Cryptodira turtles are known for their diverse adaptations, allowing them to thrive in different ecological niches around the globe.