Heliozoa
Encyclopedia
Heliozoa are phagotrophs. They are roughly spherical amoeboid
s with many stiff, microtubule
-supported projections called axopods radiating outward from the cell surface. These give them the characteristic sun-like appearance for which they are named, 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 fresh water and marine environments.
The primary groups include:
Other groups include:
Several nucleariid
s were once considered heliozoa, but they do not have microtubule-supported axopods and so are now considered filose amoeboids instead.
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...
s with many stiff, microtubule
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...
-supported projections called axopods radiating outward from the cell surface. These give them the characteristic sun-like appearance for which they are named, 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 fresh water and marine environments.
Groups
Originally the heliozoa were treated together as a formal class Heliozoa or Heliozoea, but it has been realised that they are polyphyletic, as the various orders show notable differences and are no longer believed to be related. Instead, heliozoa is regarded as a descriptive term applying to various lines of protists.The primary groups include:
- Actinophryida (currently in Chromalveolata)
- Centrohelida (some support for HacrobiaHacrobiathumb|upright|The [[coccolithophore]] [[Gephyrocapsa]] oceanicaThe Cryptomonads-haptophytes assemblage is a monophyletic grouping of chromalveolata that are not included in the SAR supergroup.The term "Hacrobia" has been proposed for this group...
) - Desmothoracida (currently in RhizariaRhizariaThe 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...
)
Other groups include:
- Heliomonadida
- Gymnosphaerida
- SticholoncheSticholoncheSticholonche is a genus of protozoan with a single species, S. zanclea, found in open oceans at depths of 99-510 metres. It is generally considered a heliozoan, placed in its own order, called the Taxopodida...
Several nucleariid
Nucleariid
The nucleariids are a group of amoebae with filose pseudopods, known mostly from soils and freshwater. They are distinguished from the similar vampyrellids mainly by having mitochondria with discoid cristae.-Classification:...
s were once considered heliozoa, but they do not have microtubule-supported axopods and so are now considered filose amoeboids instead.
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/