The sarcomastigophora (the flagellates) represents protozoa that have a one to several large flagella. They are often grouped for the purposes of medicine on the basis of where they are found, and thus, two groups are considered: The mucosalflagellates and the flagellates of blood and tissues. The mucosoflagellates are not a "natural" grouping, but rather a useful collection of parasites that live in the digestive tract. The blood and tissue flagellates is a group composed of "related" parasites, i.e., trypanosomes and leishmanial organisms, that have morphologically similar stages as part of their life cycle.