Heliozoa, commonly known as sun-animalcules, are microbial
eukaryotes
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
(
protists
A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the excl ...
) with stiff arms (
axopodia
A pseudopod or pseudopodium (plural: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filament ...
) radiating from their spherical bodies, which are responsible for their common name.
The axopodia are microtubule-supported projections from the
amoeboid cell body, and are variously used for capturing food, sensation, movement, and attachment. They are similar to
Radiolaria, but they are distinguished from them by lacking central capsules and other complex skeletal elements, although some produce simple scales and spines.
They may be found in both
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
and
marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military
* ...
environments.
Classification
Originally the heliozoa were treated together as a formal taxon Heliozoa or Heliozoea, with the rank of class or phylum, but it has been realised that they are
polyphyletic, as the various orders show notable differences and are no longer believed to be descended from a single common ancestor. Instead, "heliozoa" is regarded as a descriptive term applying to various lines of protists.
The primary groups include:
*
Actinophryida
The actinophryids are an order of heliozoa, a polyphyletic array of stramenopiles, having a close relationship with pedinellids and ''Ciliophrys''. They are common in fresh water and occasionally found in marine and soil habitats. Actinophryids a ...
,
Pedinellid
Pedinellales is a group of single-celled algae found in both marine environments and freshwater.
These are found in both freshwater and marine environments, and most genera are sessile, attached by posterior stalks. The flagellum is at the ante ...
a and
Ciliophryida (currently in
Stramenopiles)
*
Centrohelida
The centrohelids or centroheliozoa are a large group of heliozoan protists. They include both mobile and sessile forms, found in freshwater and marine environments, especially at some depth.
Characteristics
Individuals are unicellular and spher ...
(some support for
Hacrobia)
*
Desmothoracida,
Heliomonadida/Dimorphida and
Gymnosphaerida (currently in
Rhizaria >
Cercozoa
Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eu ...
)
*
Taxopodida/''
Sticholonche'' (currently in
Rhizaria >
Radiolaria)
*
Rotosphaerida (currently in
Opisthokonta >
Nucleariida
Nucleariida is a group of amoebae with filose pseudopods, known mostly from soils and freshwater. They are distinguished from the superficially similar vampyrellids mainly by having mitochondria with discoid cristae, in the absence of superfic ...
and in
Rhizaria)
Several
nucleariid
Nucleariida is a group of amoebae with filose pseudopods, known mostly from soils and freshwater. They are distinguished from the superficially similar vampyrellids mainly by having mitochondria with discoid cristae, in the absence of superfici ...
s were once considered heliozoa, but they do not have microtubule-supported axopods and so are now considered filose amoeboids instead.
References
External links
* ''Actinosphaerium'' (single-celled) is an example of a heliozoa. For an image see http://www.microscopy-uk.org.uk/index.html?http://www.microscopy-uk.org.uk/ponddip/
*
Obsolete eukaryote taxa
Eukaryote orders
{{Eukaryote-stub