Percolozoa
Encyclopedia
The Percolozoa are a group of colourless protozoa
, including many that can transform between amoeboid
, flagellate
, and encysted stages.
. The entire group is usually called the Heterolobosea, but this may be restricted to members with amoeboid stages.
One Heterolobosea classification system is as follows:
Pleurostomum flabellatum has recently been added to Heterolobosea.
, which can become pathogenic in humans and is often fatal. The group is closely related to the Euglenozoa
, and share with them the unusual though not unique characteristic of having mitochondria
with discoid crista
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
group.
The amoeboid stage is roughly cylindrical, typically around 20-40 μm
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
s, but the amoebae only aggregate as individuals or in small groups and do not die to form the stalk.
created the phylum Percolozoa for the extended group, together with the enigmatic flagellate Stephanopogon
.
Cavalier-Smith maintained the Heterolobosea as a class for amoeboid forms. He has defined Percolozoa as "Heterolobosea plus Percolatea classis nov."
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
, including many that can transform between amoeboid
Amoeboid
Amoeboids are single-celled life-forms characterized by an irregular shape."Amoeboid" and "amœba" are often used interchangeably even by biologists, and especially refer to a creature moving by using pseudopodia. Most references to "amoebas" or "amoebae" are to amoeboids in general rather than to...
, flagellate
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...
, and encysted stages.
Terminology and classification
These are collectively referred to as schizopyrenids, amoeboflagellates, or vahlkampfids. They also include the acrasids, a group of social amoebae that aggregate to form sporangiaSporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
. The entire group is usually called the Heterolobosea, but this may be restricted to members with amoeboid stages.
One Heterolobosea classification system is as follows:
- SchizopyrenidaSchizopyrenidaSchizopyrenida is an order of Heterolobosea.It contains Naegleria fowleri....
- VahlkampfiidaeVahlkampfiidaeVahlkampfiidae is a family of Heterolobosea.It includes the following genera:* Monopylocystis* Naegleria* Neovahlkampfia* Paravahlkampfia* Psalteriomonas* Sawyeria* Tetramitus* Vahlkampfia* Willaertia...
- GruberellidaeGruberellidaeGruberellidae is a family of Heterolobosea....
- Vahlkampfiidae
- Acrasida
Pleurostomum flabellatum has recently been added to Heterolobosea.
Characteristics
Most Percolozoa are found as bacterivores in soil, freshwater, and on feces. There are a few marine and parasitic forms, including the species Naegleria fowleriNaegleria fowleri
Naegleria fowleri is a free-living excavate form of protist typically found in warm bodies of fresh water, such as ponds, lakes, rivers, and hot springs. It is also found in soil, near warm-water discharges of industrial plants, and unchlorinated swimming pools in an amoeboid or temporary...
, 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. There are two main subgroups, the euglenids and kinetoplastids...
, 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 eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
with discoid 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 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 kingdom of unicellular eukaryotes, often known as Excavata. The phylogenetic category Excavata, proposed by Cavalier-Smith in 2002, contains a variety of free-living and symbiotic forms, and also includes some important parasites of humans.-Characteristics:Many excavates...
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 m and 10−4 m .Distances shorter than 10 µm* 10 µm — width of cotton fibre...
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
Percolomonas
Percolomonas is a genus of free-living flagellate Heteroloboseans, forming a clade with Stephanopogon.It includes the species Percolomonas cosmopolitus....
, Lyromonas
Lyromonas
Lyromonas is an Excavata genus.It has one known species....
, and Psalteriomonas
Psalteriomonas
Psalteriomonas is a genus of amoebae in the group of Heterolobosea....
are known only as flagellates, while Vahlkampfia
Vahlkampfia
Vahlkampfia is an genus of amoeboids in Heterolobosea....
, Pseudovahlkampfia
Pseudovahlkampfia
Pseudovahlkampfia is an Excavata genus.It includes the species Pseudovahlkampfia emersoni....
, 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.-Slug behavior:When food 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.
History
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-SmithThomas Cavalier-Smith
Professor Thomas Cavalier-Smith , FRS, FRSC, NERC 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.-Characteristics:It closely resembles certain ciliates and was originally classified with them, but is now considered a flagellate. The cell is somewhat flattened, with multiple smooth flagella arranged in rows running from the front to the back, and...
.
Cavalier-Smith maintained the Heterolobosea as a class for amoeboid forms. He has defined Percolozoa as "Heterolobosea plus Percolatea classis nov."