The Cryptodira can withdraw their head into its shells by bending its head vertically in an "S-shape" by the vertebral column (Gruyter 252). They have a different plate structure where "inframarginal plates" divide the carapace from the plastron of a turtle (Gruyter 252). The "pelvic girdles" of the Cryptodira are not connected with the "plastron" (Gruyter 252).
The second suborder is the Pleurodira. There are only two families in this suborder, the Pelomedusidae, and Chelidae. According to the Concise Encyclopedia of Biology, the turtles within this suborder are "superior" to their Cryptodira counterparts (Gruyter 252). They are primarily sea turtles such as the Chelonia mydas, which is the green sea turtle or the Eretmochelysimbricata which is the hawksbill turtle under the Chelidae family. The turtles rear their heads in sideways when going into the shelter of their shells (Gruyter 252). The inframarginal plates were "reduced" to an "anterior plate" and "posterior plate" at the groin area or behind their forelegs or the turtles have none at all (Gruyter 252). Finally, their pelvic girdles are connected, unlike these of the turtles of the Cryptodira order (Gruyter 252).
There are many regions where the families reside in. Like many animals, turtles evolved over the years to adapt to their environments. This is what sets each of the families apart. The turtles that have evolved to live on land and turtles that evolved to live in the vas oceans. Turtles can be further broken into which regions they inhabit. The turtles of two regions that stand out the most are the turtles live in these two regions, the Palearctic sub region and the seas and oceans. There are three major differences between the two areas of these turtles: species diversities, their locations, and the size of their carapaces.
The first major difference is the diversity of turtle's species that live in each area.