Transference of the South American opossums hemoparasite Nuttallia brasiliensis to the genus Babesia are discussed and proposed due to the pre-occupation of Nuttallia genus by mollusk species, as well as the synonym of Theileria brasiliensis to Babesia brasiliensis. Simultaneously the situation of the others members of Nuttallia and Achromaticus genus is discussed, in relation with the international rules of nomenclature and its common biologic and morphologic aspects. Also a chronological summary of B. brasiliensis reports is given