Thediplomonadsare a group offlagellates, most of which are parasitic. They include most notablyGiardia lamblia, which causesgiardiasisin humans. They are placed among themetamonads, and appear to be particularly close relatives of theretortamonads.
Most diplomonads are double cells: they have twonuclei, each with four associated flagella, arranged symmetrically about the body's main axis. Like the retortamonads, they lack bothmitochondriaand aGolgi apparatus. However they are now known to possess mitochondrial relics, calledmitosomes. These are not used inATPsynthesis the way mitochondria are, but are involved in the maturation ofiron-sulfur proteins
