Three alternative hypotheses for the observed distribution of parasitic and free-living lifestyles within the Diplomonadida in relation to the outgroup Chilomastix, a retortomonad genus, are presented in Figure 3.
It appears then, that enteric parasites have produced free-living descendants at least twice in the evolution of the Diplomonadida. We are, at present, unaware of any other demonstration of the adaptation to a free-living habit from obligately endoparasitic ancestors.
Examination of some of the character state transformations in the phylogenetic analysis of the Diplomonadida (see Siddall et al., 1992) illuminates how some diplomonads are able to pursue a free-living mode without mitochondria.
The present result showed four protozoan-species, as cysts, Giardia lamblia (Diplomonadida
, Hexamitidae), Cryptosporidium parvum (Eucoccidiorida, Cryptosporidiidae), Cyclospora cayatenensis (Eucoccidiorida, Eimeriidae) and Entamoeba coli (Archamoebae).