Breviatea

Breviatea, commonly known as breviate amoebae, are a group of free-living, amitochondriate protists with uncertain phylogenetic position. They are biflagellate, and can live in anaerobic (oxygen-free) environments. They are currently placed in the Obazoa clade. They likely do not possess vinculin proteins. Their metabolism relies on fermentative production of ATP as an adaptation to their low-oxygen environment.

The lineage emerged roughly one billion years ago, at a time when the oxygen content of the Earth's oceans was low, and they thus developed anaerobic lifestyles. Together with Apusomonads, they are the closest relatives of the Opisthokonts, a group that includes animals and fungi.