The Pleurodira are one of the two living suborders of turtles, the other being the Cryptodira. In many cases in the nomenclature of animals, ranks such as suborder are considered of little importance apart from nomenclatural or taxonomic reasons. However, this is not the case with the suborders of the turtles. This division represents a very deep evolutionary divide between two very different types of turtles. The physical differences between them, although anatomical and largely internal, are nonetheless significant, and the zoogeographic implications of them are substantial. The Pleurodira are known more commonly as the side-necked turtles and the name Pleurodira quite literally translates to side neck, whereas the Cryptodira are known as hidden-necked turtles. The Pleurodira turtles are restricted to the Southern Hemisphere, largely to Australia, South America, and Africa. Within the Pleurodira, two living families are represented: Chelidae, also known as the Austro-South American side-necked turtles, and the Pelomedusidae, also known as the Afro-South American side-necked turtles.