Trichomonad

The trichomonads are an order of anaerobic protists, included with the parabasalids. Most are either parasites or other endosymbionts of animals. They typically have four to six flagella at the cell's apical pole, one of which is recurrent - that is, it runs along a surface wave, giving the aspect of an undulating membrane. Like other parabasalids they typically have an axostyle, pelta, costa and parabasal bodies. In Histomonas there is only one flagellum and a reduced axostyle, and in Dientamoeba both are absent.

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Trichomonads reproduce by a special form of longitudinal fission, leading to large numbers of trophozoites in a relatively short time. Cysts never form, so transmission from one host to another is always based on direct contact between the sites they occupy.

Some organisms in this order include:

• Trichomonas vaginalis, an organism living inside the vagina of humans
• Dientamoeba fragilis, parasitic ameboid in humans
• Histomonas meleagridis, parasite that causes blackhead disease in poultry.
• Mixotricha paradoxa, a symbiotic organism inside termites, host of endosymbionts.