Archamoebae

The Archamoebae are an important group of amoebae. They are unusual among protists because they have no mitochondria. 
The group includes many genera which are internal parasites or commensals of animals: for example "Entamoeba" and "Endolimax". Some are human pathogens, causing diseases such as amoebic dysentery. Other genera of archamoebae live in freshwater habitats, and have flagella. Most have a single nucleus and flagellum, but the giant amoeba "Pelomyxa" has many of each.
Analysis of 100 genes shows that the Archamoebae are part of the Amoebozoa which have lost their mitochondria. They are close relatives of the slime moulds. Parasitic and commensal forms like "Entamoeba" and "Endolimax" developed separately from free-living ancestors.