The order includes species of shearwaters, albatrosses, petrels and storm-petrels. They are exclusively marine birds and have the widest geographical distribution of all birds. Some species of petrels travel thousands of kilometres from their continental colonies to their breeding grounds on the edge of Antarctica. The feature shared by Procellariformes is the presence of tubular nostrils that contain salt glands, which are essential for osmoregulation in these marine birds. This order includes one of the birds with the largest wingspan in the world, the great albatross (Diomedea exulans), which can reach 3.5 metres. Such a wingspan allows it to glide over very long distances on the sea winds. The Procellariformes are the sister group to the Sphenisciformes (penguins and rockhoppers).