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 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. Vectors include ticks and leeches.

Evolution

A Bayesian analysis based on the nuclear genes suggests a date of divergence between Babesia and Theileria of

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.
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.
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
Family Garniidae
Family Theileriidae
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:
Recognised synonyms of the genus Nicollia - which is now itself regarded as a synonym of Babesia - include:
Recognised synonyms of the genus Theileria include: