Oxymonad

The Oxymonads are a group of flagellated protozoa found exclusively in the intestines of termites and other wood-eating insects. Along with the similar parabasalid flagellates, they harbor the symbiotic bacteria that are responsible for breaking down cellulose. Both groups lack mitochondria, and oxymonads also lack dictyosomes.

Most Oxymonads are around 50 &mu;m in size and have a single nucleus, associated with four flagella. Their basal bodies give rise to a several long sheets of microtubules, which form an organelle called an axostyle, but different in structure from the axostyles of parabasalids. The cell may use the axostyle to swim, as the sheets slide past one another and cause it to undulate. An associated fiber called the preaxostyle separates the flagella into two pairs. A few oxymonads have multiple nuclei, flagella, and axostyles.

The free-living flagellate Trimastix is closely related to the oxymonads. It lacks mitochondria and has four flagella separated by a preaxostyle, but unlike the oxymonads has a feeding groove. This character places the Oxymonads and Trimastix among the excavates, and in particular they may belong to the metamonads.