The retortamonads are a small group of

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their ...

s, most commonly found in the intestines of animals as

commensals Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

, although a free-living species called the ''Chilomastix cuspidata'' exists. They are grouped under the taxon, Archezoa. They are usually around 5-20 μm in length, and all of their small subunit ribosomal RNA gene sequences are very similar to each other. There are two genera: '' Retortamonas'' with two flagella, and '' Chilomastix'' with four. In both cases there are four basal bodies anterior to a prominent feeding groove, and one flagellum is directed back through the cell, emerging from the groove. The retortamonads lack

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

, golgi apparatus, dictyosomes, and peroxisomes. They are close relatives of the

diplomonad The diplomonads (Greek for "two units") are a group of flagellates, most of which are parasitic. They include ''Giardia duodenalis'', which causes giardiasis in humans. They are placed among the metamonads, and appear to be particularly close r ...

s, and are placed among the metamonads along with them. Due to the abundant phylogenetic similarities between the two flagellates, since diplomonads do not ancestrally lack mitochondrion, this suggests that retortamonads are also secondarily amitochondriate.

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