They include the retortamonads, diplomonads, parabasalids, oxymonads, and a range of more poorly studied taxa, most of which are free-living flagellates.

However, they are now known to have lost aerobic mitochondria secondarily, and retain both organelles and nuclear genes derived ultimately from the mitochondrial endosymbiont genome.

Mitochondrial relics include hydrogenosomes, which produce hydrogen (and make ATP), and small structures called mitosomes.

The metamonads were thought to make up part of the Excavata, a proposed eukaryotic supergroup including flagellates with feeding grooves and their close relatives.

The other branch contains two large groups: the Fornicata, which is closely related to barthelonids[1] and the recently isolated Skoliomonas;[3] and the Preaxostyla.