Apusozoa
Encyclopedia
The Apusozoa are a phylum comprising 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.
The name derives from the Greek words for footless (απους) and animal (ζώο).
It has been suggested that Mantamonas be classified in Apusozoa.
The form of the mitochondria
varies between the different orders. Among the apusomonads they have tubular crista
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.
s is uncertain.
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.
Cavalier-Smith, in a collaborative paper with Alexandra Stechmann, postulated that Apusozoa belongs in the bikont
clade. It may be one of the most divergent bikont lineages.
It has more recently been grouped with the unikont
s. It has been suggested that it may be related to the opisthokont
group.
Flagellate
Flagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...
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
Theca
A theca refers to any case, covering, or sheath.In botany, the theca of an angiosperm consists a pair of microsporangia that are adjacent to each other and share a common area of dehiscence called the stomium. Any part of a microsporophyll that bears microsporangia is called an anther. Most...
under the dorsal surface of the cell.
The name derives from the Greek words for footless (απους) and animal (ζώο).
Classification
There are three orders, often treated as separate groups: the apusomonads, ancyromonads, and hemimastigids.| Name | Genera | Flagella | Mitochondrial cristae |
|---|---|---|---|
| apusomonads | Apusomonas Apusomonas Apusomonas is a genus of Apusozoa.It includes the species Apusomonas proboscidea.... and Amastigomonas Amastigomonas Amastigomonas is a genus of Apusozoa.This genus has been divided into five different genera including Podomonas, Manchomonas, and Multimonas.Several species have been described including:... . Some sources further subdivide this group. |
biflagellate | tubular |
| ancyromonads | Ancyromonas Ancyromonas Ancyromonas is a genus of Apusozoa. It is a flagellate.It includes the species Ancyromonas sigmoides.Planomonas has been described as a junior synonym of Ancyromonas.... |
biflagellate | flat |
| hemimastigids (also called the spironemids or Hemimastigophora) | Hemimastix, Spironema, and Stereonema | multiflagellate | tubular |
It has been suggested that Mantamonas be classified in Apusozoa.
Characteristics
The apusomonads and ancyromonads 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. By contrast, hemimastigids cell has multiple flagella, arranged in rows from the anterior of the cell towards the posterior.The form of the mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
varies between the different orders. Among the apusomonads they have tubular crista
Crista
Cristae are the internal compartments formed by the inner membrane of a mitochondrion. They are studded with proteins, including ATP synthase and a variety of cytochromes. The maximum surface for chemical reactions to occur is within the mitochondria...
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.
Relationship to other eukaryotes
On molecular trees, the apusomonads and ancyromonads group together, but their relationship to other eukaryoteEukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
s is uncertain.
Although it has sometimes been included in the Rhizaria
Rhizaria
The Rhizaria are a species-rich supergroup of unicellular eukaryotes. This supergroup was proposed by Cavalier-Smith in 2002. They vary considerably in form, but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods...
, based on 18S rRNA gene sequencing, it has been concluded that the Apusozoa are not closely related to other Rhizaria.
Cavalier-Smith, in a collaborative paper with Alexandra Stechmann, postulated that Apusozoa belongs in the bikont
Bikont
A Bikont is a eukaryotic cell with two flagella, as its name suggests. It is a division of eukaryotes.-Enzymes:Another shared trait of bikonts is the fusion of two genes into a single unit: the genes for thymidylate synthase and dihydrofolate reductase encode a singleprotein with two...
clade. It may be one of the most divergent bikont lineages.
It has more recently been grouped with the unikont
Unikont
Unikonts are members of the Unikonta, a taxonomic group proposed by Thomas Cavalier-Smith.It includes amoebozoa, opisthokonts, and Apusozoa.-Clade:...
s. It has been suggested that it may be related to the opisthokont
Opisthokont
The opisthokonts or "Fungi/Metazoa group" are a broad group of eukaryotes, including both the animal and fungus kingdoms, together with the eukaryotic microorganisms that are sometimes grouped in the paraphyletic phylum Choanozoa...
group.