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The Percolozoa are a group of colourless protozoa
Protozoa

Protozoan are microorganisms classified as unicellular eukaryotes. While there is no exact definition of the term "protozoan", most scientists use the word to refer to a unicellular heterotrophic protist, such as an amoeba or a ciliate....
, including many that can transform between amoeboid
Amoeboid

Amoeboids are unicellular life-forms characterized by their similarity to amoebas....
, flagellate
Flagellate

Flagellates are cell s with one or more whip-like organelles called flagellum. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla....
, and encysted stages. These are collectively referred to as schizopyrenids, amoeboflagellates, or vahlkampfids. They also include the acrasids, a group of social amoebae that aggregate to form sporangia
Sporangium

A sporangium is a plant or fungus structure producing and containing spores. Sporangia occur in Flowering plant, gymnosperms, ferns, fern allies, bryophytes, Algaee, and Fungus....
. The entire group is usually called the Heterolobosea, but this may be restricted to members with amoeboid stages.

Most Percolozoa are found as bacterivores in soil, freshwater, and on feces.






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The Percolozoa are a group of colourless protozoa
Protozoa

Protozoan are microorganisms classified as unicellular eukaryotes. While there is no exact definition of the term "protozoan", most scientists use the word to refer to a unicellular heterotrophic protist, such as an amoeba or a ciliate....
, including many that can transform between amoeboid
Amoeboid

Amoeboids are unicellular life-forms characterized by their similarity to amoebas....
, flagellate
Flagellate

Flagellates are cell s with one or more whip-like organelles called flagellum. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla....
, and encysted stages. These are collectively referred to as schizopyrenids, amoeboflagellates, or vahlkampfids. They also include the acrasids, a group of social amoebae that aggregate to form sporangia
Sporangium

A sporangium is a plant or fungus structure producing and containing spores. Sporangia occur in Flowering plant, gymnosperms, ferns, fern allies, bryophytes, Algaee, and Fungus....
. The entire group is usually called the Heterolobosea, but this may be restricted to members with amoeboid stages.

Most Percolozoa are found as bacterivores in soil, freshwater, and on feces. There are a few marine and parasitic forms, including the species Naegleria fowleri
Naegleria fowleri

Naegleria fowleri is a free-living excavate form of protist typically found in warm fresh water, from 25?35 degrees Celsius in an amoeboid or temporary flagellate stage....
, which can become pathogenic in humans and is often fatal. The group is closely related to the Euglenozoa
Euglenozoa

The Euglenozoa are a large group of flagellate protozoa. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans....
, and share with them the unusual though not unique characteristic of having mitochondria
Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryote cell . These organelles range from 0.5–10 micrometers in diameter....
 with discoid crista
Crista

Cristae are the internal compartments formed by the Inner mitochondrial membrane of a mitochondrion. They are studded with proteins, including ATP synthase and a variety of cytochromes....
e. The presence of a ventral feeding groove in the flagellate stage, as well as other features, suggests that they are part of the excavate
Excavate

The excavates are a major assemblage of protists, often known as Excavata. The phylogenetic category Excavata contains a variety of free-living and symbiotic forms, and includes some important parasites of humans....
 group.

The amoeboid stage is roughly cylindrical, typically around 20-40 µm
1 E-5 m

To help compare different orders of magnitude, this page lists lengths between 10−5 metre and 10−4 m .1 E-6 m...
 in length. They are traditionally considered lobose amoebae, but are not related to the others and unlike them do not form true lobose pseudopods. Instead, they advance by eruptive waves, where hemispherical bulges appear from the front margin of the cell, which is clear. The flagellate stage is slightly smaller, with two or four anterior flagella anterior to the feeding groove.

Usually the amoeboid form is taken when food is plentiful, and the flagellate form is used for rapid locomotion. However, not all members are able to assume both forms. The genera Percolomonas, Lyromonas, and Psalteriomonas are known only as flagellates, while Vahlkampfia, Pseudovahlkampfia, and the acrasids do not have flagellate stages. As mentioned above, under unfavourable conditions, the acrasids aggregate to form sporangia. These are superficially similar to the sporangia of the dictyostelid
Dictyostelid

The dictyostelids are a group of cellular slime molds, or social amoebae. When food, normally bacteria, is readily available they are individual amoebae, which feed and divide normally....
s, but the amoebae only aggregate as individuals or in small groups and do not die to form the stalk.

The Heterolobosea were first defined by Page and Blanton in 1985 as a class of amoebae, and so only included those forms with amoeboid stages. Cavalier-Smith
Thomas Cavalier-Smith

Professor Thomas Cavalier-Smith , Royal Society, Royal Society of Canada, Natural Environment Research Council Professorial Fellow, is a Professor of Evolutionary Biology in the Department of Zoology, at the University of Oxford....
 created the phylum Percolozoa for the extended group, together with the enigmatic flagellate Stephanopogon
Stephanopogon

Stephanopogon is a peculiar marine protozoan. It closely resembles certain ciliates and was originally classified with them, but is now considered a flagellate....
. He maintained the Heterolobosea as a class for amoeboid forms, but most others have expanded them to include the flagellates as well.

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