Cryptodira

Cryptodira is a suborder of turtles, characterized by their ability to retract their heads into their shells by bending their necks in a vertical plane, earning them the nickname "S-necked" or "vertical-necked" turtles. This contrasts with the other suborder, Pleurodira (side-necked turtles), which tuck their heads to the side.123

The suborder Cryptodira encompasses approximately 263 species across 11 families, including tortoises, sea turtles, snapping turtles, and softshell turtles. These turtles are found on all continents except Antarctica and inhabit tropical and subtropical oceans, seas, and freshwater environments. Their shells, a key adaptation for protection, are formed from fused vertebrae, ribs, and dermal bones.42