The Apusozoa are an

Obazoa Obazoa (Brown et al., 2013) is a proposed sister clade of Amoebozoa (which together form Amorphea). Obazoa is composed of Breviatea, Apusomonadida and Opisthokonta. The term Obazoa is based on the OBA acronym for Opisthokonta, Breviatea, and A ...

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature ...

comprising several genera of

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and thei ...

eukaryotes. They are usually around 5–20 μm in size, and occur in soils and aquatic habitats, where they feed on

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

. They are grouped together based on the presence of an organic shell or

theca In biology, a theca (plural thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a comm ...

under the dorsal surface of the cell. The name derives from the Ancient Greek words for footless () and animal (). This phylum is currently defined as containing the

Breviata ''Breviata anathema'' is a single-celled flagellate amoeboid eukaryote, previously studied under the name '' Mastigamoeba invertens''. The cell lacks mitochondria but has remnant mitochondrial genes, and possesses an organelle believed to be a modi ...

and the

Apusomonadida The Apusomonadida are a group of protozoan zooflagellates that glide on surfaces, and mostly consume prokaryotes. They are of particular evolutionary interest because they appear to be the sister group to the Opisthokonts, the clade that inclu ...

. However, it currently usually is viewed as paraphyletic, with the Breviata as more basal. The opisthokonts appear to have emerged as sister of the apusomonadida. It has been suggested that the

Mantamonadida The Mantamonadidae are of free-living heterotrophic flagellates that move primarily by gliding on surfaces (rather than swimming). There is one genus, '' Mantamonas''. It has been suggested previously that the Mantamonadidae be classified in A ...

be classified in Apusozoa. The ancyromonadida appear to be Varisulca, Planomonadida, shifting them possibly more basal than the Amoebozoa, or less basal. While some classification systems have placed

Hemimastigida Spironemidae is a family of heterotrophic flagellates, in the group Hemimastigophora. They vary in size and shape from the ellipsoid '' Hemimastix amphikineta'' (14 × 7 μm) to the vermiform '' Spironema terricola'' (43 × 3 μm), and ...

in Apusozoa, 2018 research indicated that

hemimastigote Hemimastigophora is a group of single-celled eukaryotic organisms with a single family, Spironemidae, first identified in 1988. Over the next 30 years, different authors proposed placing these organisms in various branches of the eukaryotes. ...

s (/

Hemimastix Spironemidae is a family of heterotrophic flagellates, in the group Hemimastigophora. They vary in size and shape from the ellipsoid '' Hemimastix amphikineta'' (14 × 7 μm) to the vermiform '' Spironema terricola'' (43 × 3 μm), and ...

Spironemidae Spironemidae is a family of heterotrophic flagellates, in the group Hemimastigophora. They vary in size and shape from the ellipsoid '' Hemimastix amphikineta'' (14 × 7 μm) to the vermiform '' Spironema terricola'' (43 × 3 μm), and ...

) are their own

supra-kingdom In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla. Traditionally, some textbooks from the United States and Canada used a system of six kingdoms (Animalia, Plant ...

Characteristics

The apusomonads 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 form of the

mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...

varies between the different orders. Among the apusomonads they have tubular

crista A crista (; plural cristae) is a fold in the inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large amount of surface area fo ...

e, 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.

References

External links

Amorphea phyla Taxa named by Thomas Cavalier-Smith {{Unikont-stub