Most diplomonads are double cells: they have two nuclei, each with four associated flagella, arranged symmetrically about the body's main axis. Like the retortamonads, they lack both mitochondria and a Golgi apparatus. However they are now known to possess modified mitochondria, in the case of G. lambia, called mitosomes. These are not used in ATP synthesis the way mitochondria are, but are involved in the maturation of iron-sulfur proteins.
^Tovar J, León-Avila G, Sánchez LB et al. (2003). "Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation". Nature426 (6963): 172–6. doi:10.1038/nature01945. PMID14614504.