Achromatorida

Achromatorida is an order of non-pigmented intraerythrocytic parasitic alveolates belonging to the subclass Haemosporidiasina. The order was created by Jacques Euzéby in 1988.

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.

Description

These are minute rounded or pyriform parasites found within erythrocytes, or other circulating or endothelial cells of vertebrates. The parasites reproduce by merogony without oocysts or spores.

The apical complex has a polar ring and rhoptries. 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.

Evolution

A Bayesian analysis based on the nuclear genes suggests a date of divergence between ''Babesia'' and ''Theileria'' of ( 95% credible interval –)

Taxonomy

This order is divided into two suborders:

Suborder Babesiina

These are agents of piroplasmosis ''sensu stricto''. The species have been placed into two families.

Family Babesiidae Poche 1913

This family excludes species that undergo schizogony in lymphocytes before parasitizing erythrocytes. these species have been placed in the genus ''Theileria''.

Species in this family have rhoptries, a polar ring and subpellicular tubules in its apical complex. With the exception of the genus ''Tunetella'' which infects tortoises, species in this family 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 '' Rangelia''
*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

The genus ''Nephromyces'' may also belong to this family.

Suborder Theileriina

These are parasites of erythrocytes and diverse white blood cells with sexual reproduction by exoerythrocytic or by exo- and endoerythrocytic schizogony.

Family Leucocytozoidae
*Genus ''Leucocytozoon'' Ziemann 1898
**Subgenus Leucocytozoon
**Subgenus Akiba

Family Garniidae
*Genus ''Fallisia'' Lainson, Landau & Shaw 1974
**Subgenus Fallisia
**Subgenus Plasmodioides
*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

Notes

There are also a number of genera of uncertain placement that earlier were provisionally included in this taxon:

'' Elleipsisoma'' Franca 1912: This genus is currently placed in the ''Eimeriorina''. Its placement there is unusual given that species in this genus infect erythrocytes.

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 genus ''Nicollia'' Franca 1910 is now regarded as a synonym for ''Babesia''.

'' Cytauxzoon'' replicates in macrophages rather than in lymphocytes. For this reason may be moved to a new family at some point.

'' Pirhemocyton'' was described as a protozoan infecting lizards but the intraerythrocytic inclusions have since been shown to be due to a viral infection.

An additional genus - '' Chelonplasma'' - has been described but its taxonomic status is unclear.

Synonyms

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
*''Apiosoma''
*''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
*''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:

*''Gonderia''

Notes

'' 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'')

References

{{Taxonbar, from=Q4673905

Apicomplexa orders