(order Kinetoplastida), any of an order of protozoan zooflagellates characterized as free-living or parasitic colourless organisms, typically with one or two flagella and usually without a secreted pellicle (or envelope). Solitary and colonial free-living forms usually feed by pseudopodia (protoplasmic extensions) or by a simple mouth; parasitic forms absorb food through the cell wall. Reproduction is by a lengthwise splitting, although multiple division and budding occur, and sexual reproduction has been reported.

Protomonads, such as the solitary Monas or the colonial Anthophysis, are oval and amoeboid with one to three flagella; they inhabit foul water and feces and also may be found in human and animal intestines. The choanoflagellates (choanoflagellate), which sometimes are placed in a separate order, have a food-catching collar surrounding a single flagellum. The Bodo group includes forms with two to four flagella. The Trypanosoma species are elongated blood parasites found in man and many animals. The members of the vertebrate parasite genus leishmania also cause disease.