[3][4] They divide by binary fission and as sporozoan parasites they possess sexual and asexual phases (sexual reproduction occurs in the tick gut[5]).

[6][7] They are minute rounded or pyriform parasites found within erythrocytes, or other circulating or endothelial cells of vertebrates, where they reproduce by merogony.

The trophozoite stage is separated from erythrocyte by a single membrane.

An apical complex with a polar ring and rhopteries occurs, but without a conoid and usually without associated pellicular microtubules.

They lack flagella and do not form either oocysts or spores.