The taxonomy of these organisms has been one of some controversy. Weylon in 1926 grouped many of these genera into the genus Babesia - given what is now known about these genera this was probably an error. Agreement on the organisation of these genera probably cannot be regarded as being settled.
The apical complex has a polar ring and rhopteries. A conoid is lacking and most species lack the associated pellicular microtubules. Flagellae are lacking. The trophozoite stage is separated from erythrocyte by single membrane (in the other groups there usually 2 or more). Vectors include ticks and leeches.
This order is divided into two suborders:
Family Babesiidae Poche 1913
This family excludes species that undergo schizogony in lymphocytes before parasitizing erythrocytes which belong to the genus Theileria. Species in this genus have rhoptries, a polar ring and subpellicular tubules in its apical complex. With the exception of the genus Tunetella which infects tortoises, they infect in warm-blooded vertebrates and are transmitted by ticks.
- Genus Babesia Starcovici 1893
- Genus Echinozoon Garnham 1951
- Genus Entopolypoides Mayer 1933
- Genus Microbabesia Sohns 1918
- Genus Tunetella Brumpt & Lavier 1935
Family Haemohormidiidae Levine 1984
This family includes species that infect marine animals. A notable exception is the genus Serpentoplasma which infects reptiles. Very little is known about most of these genera.
- Genus Cardiosporidium Gaver & Stephan 1907
- Genus Cristalloidophora Dehorne 1934, Porchet 1978
- Genus Dobellia Brumpt 1913
- Genus Echinococcidium Porchet 1978
- Genus Globidiellum Neumann 1909
- Genus Haemohormidium Léger & Duboscq 1910
- Genus Haematractidium Henry 1910
- Genus Joyeuxella Le Calvez 1939
- Genus Rhabdospora Landau, Boulard & Houin 1969
- Genus Serpentoplasma Pienaar 1962
- Genus Spermatobium Eisen 1895
- Genus Toxocystis Henry 1910
- Genus Trophosphaera du Toit 1938
These are parasites of erythrocytes and diverse white blood cells with sexual reproduction by exoerythrocytic or by exo- and endoerythrocytic schizogony.
- Genus Fallisia Lainson, Landau & Shaw 1974
- Genus Garnia Lainson et al 1971
- Genus Progarnia Lainson 1995
Family Theileriidae (synonym Gonderiidae)
- Genus Cytauxzoon Neitz & Thomas 1948
- Genus Theileria Bettencourt, França and Borges 1907
- Genus Haematoxenus Uilenberg 1964
There are also a number of genera of uncertain placement that earlier were provisionally included in this taxon:
The families Dactylosomatidae (genera Babesiosoma Jakowski and Nigrelli 1956 and Dactylosoma Labbé 1894) were transferred to the suborder Adeleorina by Boulard et al in 1982. The position of the Anthemosomatidae (genus Anthemosoma Landau, Boulard and Houin 1969) remains unclear.
The classification of the species in this group is difficult. Over the passage of time several genera have been described only to re classified as being synonyms of previously described genera.
Currently recognised synonyms of the genus Babesia include:
- Achromaticus Dionisi 1899
- Babesiella Mesnil 1919
- Francaiella Yakimoff 1926
- Haematococcus Babes 1888
- Luhsia Dschunkowsky 1938
- Microsoma Sohns 1918
- Nicollia Franca 1910
- Patonella Ray & Idnani 1943
- Piroplasma Patton 1895
- Pyrosoma Smith 1893
- Rangelia Carini & Maciel 1914
- Rosiella Nuttall 1912
- Sogdianella Schurenkova 1939
Recognised synonyms of the genus Nicollia - which is now itself regarded as a synonym of Babesia - include:
- Nuttallia Franca 1909
- Smithia Franca 1910
Recognised synonyms of the genus Theileria include:
Apiosoma is currently the name of a genus of ciliated protozoa also known as Glossatella. Although this genus is pathogenic to fish it has not related to the parasites in this taxon.
Nuttallia Dall 1898 is a genus of sunset clams (Psammobiidae)
- Euzéby, J. (1988) Comparative Medical Protozoology, Vol. 3: Apicomplexa, 2: Haemosporidioses, Part 1: Plasmodiids, Haemoproteids, "Piroplasms" (general characters)
- Levine ND (1984) Nomenclatural corrections and new taxa in the apicomplexan protozoa. Trans Am Micro Soc 103 (2) 195-204