The retortamonads are a small group of flagellate

Flagellate

Flagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...

s, mostly found in the intestines of animals, although some are free-living. They are usually around 5-20 μm in length. There are two genera: Retortamonas

Retortamonas

Retortamonas is a genus of flagellate protozoa that live in the intestines of various animals. Twenty-eight species have been described, mostly differentiated by the host spectrum of each species, since they are morphologically very similar. Some of the species may be synonymous, and an undescribed...

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 both mitochondria

Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...

 and golgi apparatus

Golgi apparatus

The Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....

. They are close relatives of the diplomonad

Diplomonad

The diplomonads are a group of flagellates, most of which are parasitic. They include most notably Giardia lamblia, which causes giardiasis in humans...

s, and are placed among the metamonad

Metamonad

The metamonads are a large group of flagellate protozoa. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well...

s along with them.