Cryptodira

Cryptodira [‚krip·tə′dī·rə]

(vertebrate zoology)

A suborder of the reptilian order Chelonia including all turtles in which the cervical spines are uniformly reduced and the head folds directly back into the shell.

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Cryptodira 

an order of turtles of the subclass Testudinata. The carapace consists of bony plates covered with horny scales. The neck and head can be withdrawn into the carapace by a vertical flexure of the neck.

There are 140 species, making up 30 genera from six families. The turtles represent about two-thirds of all living turtle species. The six families are Emydidae (common freshwater turtles), Kinosternidae (mud turtles and musk turtles), Chelydridae (snapping turtles), Dermatemydidae (with a single species, the Central American river turtle), Platysternidae (with a single species, the big-headed turtle), and Testudinidae (land tortoises). The USSR has two species of common freshwater turtles and two species of land tortoises.

Some zoologists consider the Cryptodira a suborder.