Preaxostyla, also known as Anaeromonadea, is a group of excavate protists, comprising the oxymonads, Trimastix, and Paratrimastix. This group is studied as a model system for reductive evolution of mitochondria, because it includes both organisms with anaerobic mitochondrion-like organelles (Trimastix and Paratrimastix), and those that have completely lost their mitochondria (oxymonads Monocercomonoides, Streblomastix, and Blattamonas).
Based on the work of Zhang et al. 2015.