The two clades with modified mitochondria are the diplomonads and the parabasalids. The diplomonads include the common and unpleasant water -borne intestinal parasite Giardia. Protists in this clade thrive in a low-oxygen environment, and do not have a functional electron transport chain.
The parabasalids, a group whose members include Trichomonas, which is a sexually transmitted parasite of the human reproductive tract, and trychonympha, a symbiotic organism found in the gut of some species of termites and ants. Members of this group do not have functional mitochondria, but they do have an organelle known as a hydrogenosome, which is believed to be a vestigial mitochondrion.
Some taxonomists group both of these clades together into the metamonads.