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Scientific classification
Domain: Eukaryota
(unranked): Bikonta
Phylum: Apusozoa
Cavalier-Smith 1997 em.


The Apusozoa are a phylum[1] comprised of several genera of flagellate protozoa. They are usually around 5-20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria. They are grouped together based on the presence of an organic shell or theca under the dorsal surface of the cell.



There are three orders, often treated as separate groups: the apusomonads, ancyromonads, and hemimastigids.

The apusomonads include two genera, Apusomonas and Amastigomonas, and the ancyromonads include one, Ancyromonas. They have two flagella inserted at right angles, near the anterior of the cell. They move by gliding, with one flagellum trailing along the side and one directed to the anterior.

The hemimastigids include three genera, Hemimastix, Spironema, and Stereonema. They are also called the spironemids or Hemimastigophora. Each cell has multiple flagella, arranged in rows from the anterior of the cell towards the posterior.


The form of the mitochondria varies between the different orders. Among the apusomonads they have tubular cristae, the ancyromonads flat cristae, and the hemimastigids ambiguous or sacculate cristae. This characteristic was originally considered a good indicator of relationships, but is now known to vary even among close relatives.


On molecular trees, the apusomonads and ancyromonads group together, but their relationship to other eukaryotes is uncertain.

Cavalier-Smith, in a collaborative paper with Alexandra Stechmann, postulated that Apusozoa belongs in the bikont clade.[2][3]

Although it has sometimes been included in the Rhizaria, based on 18S rRNA gene sequencing, it has been concluded that the Apusozoa are not closely related to other Rhizaria.

It may be one of the most divergent bikont lineages.[4]

It has also been suggested that it may be related to the opisthokont group.[5]


  1. ^ Cavalier-Smith T, Chao EE, Stechmann A, Oates B, Nikolaev S (October 2008). "Planomonadida ord. nov. (Apusozoa): ultrastructural affinity with Micronuclearia podoventralis and deep divergences within Planomonas gen. nov". Protist 159 (4): 535–62. doi:10.1016/j.protis.2008.06.002. PMID 18723395.  
  2. ^ Cavalier-Smith, T.; Stechmann, Alexandra (2003). "The root of the eukaryote tree pinpointed". Current Biology 13 (17): R665–R666. doi:10.1016/S0960-9822(03)00602-X.  
  3. ^ Cavalier-Smith T (March 2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". Int. J. Syst. Evol. Microbiol. 52 (Pt 2): 297–354. PMID 11931142.  
  4. ^ Moreira D, von der Heyden S, Bass D, López-García P, Chao E, Cavalier-Smith T (July 2007). "Global eukaryote phylogeny: Combined small- and large-subunit ribosomal DNA trees support monophyly of Rhizaria, Retaria and Excavata". Mol. Phylogenet. Evol. 44 (1): 255–66. doi:10.1016/j.ympev.2006.11.001. PMID 17174576.  
  5. ^ Cavalier-Smith T (2009). "Megaphylogeny, cell body plans, adaptive zones: causes and timing of eukaryote basal radiations". J. Eukaryot. Microbiol. 56 (1): 26–33. PMID 19340985.  

Further reading



Up to date as of January 23, 2010

From Wikispecies


Main Page
Cladus: Eukaryota
Regnum: Protista
Subregnum: Biciliata
Infraregnum: Incertae sedis
Phylum: Apusozoa
Classes: Diphyllatea - Thecomonadea


  • Thomas Cavalier-Smith, The excavate protozoan phyla Metamonada Grassé emend. (Anaeromonadea, Parabasalia, Carpediemonas, Eopharyngia) and Loukozoa emend. (Jakobea, Malawimonas): their evolutionary affinities and new higher taxa, Internat. Journal of Syst. and Evol. Microbiol. 53, 1741-1758 (2003).
  • Thomas Cavalier-Smith, Protist phylogeny and the high-level classification of Protozoa, Europ. J. Protistol. 39, 338-348 (2003).

Alternative classifications

See Thecomonadea.


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