Pancake Turtle, belonging to the Cryptodira lineage
Two current lineages are considered: Cryptodira, whose representatives are able to retract their head into the hull and Pleurodira, where representatives bend their necks horizontally to retract their heads. The first group is absent only in Australia and fits most species, including all sea turtles; the second group is found only in the Southern Hemisphere and does not have terrestrial representatives, with the tortoise being an example of an animal of this lineage.
Blood from these animals flows to the heart through the lungs, back to the heart, and then circulates to the rest of the body. As for breathing, the junction of the ribs with the hull does not allow movements in the rib cage. Its large lungs are connected to the carapace through sheets of connective tissue that attach to its viscera, making the movement of these viscera help in the expansion of the lungs in the respiratory act, through muscle contractions. Some aquatic representatives are also able to carry out gas exchange via the cloaca and pharynx.
As for social behavior, tactile signs such as bites and blows; visuals such as color patterns; and olfactory are used – and some males even vocalize during courtship. There are social hierarchies between individuals, usually marked by physical clashes, where the winner becomes the dominant.