 The inside of the carapace is often heavily buttressed.This has sometimes been seen as a defense mechanism, that is it increases the strength of the shell against biting force, however Thomson (2003) demonstrated it is linked to feeding methods and the prevention of internal torsion of the shell.Chelids also lack mesoplastra, which separates them from the Pelomedusidae.The cervical scute is usually present, though it is absent in some species of "Elseya" and "Myuchelys".