Heliozoa

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Heliozoa
First ever heliozoan depiction by Louis Joblot.png
Heliozoan depicted by Louis Joblot, 1718
Scientific classification OOjs UI icon edit-ltr.svg
(obsolete)
Kingdom: Chromista
Subkingdom: Hacrobia
Phylum: Heliozoa
Haeckel, 1866
Classes [1]

Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (axopodia) radiating from their spherical bodies, which are responsible for their common name. [2] [3] [4] 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. [5] They may be found in both freshwater and marine environments.

Contents

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: [6]

Several nucleariids were once considered heliozoa, but they do not have microtubule-supported axopods and so are now considered filose amoeboids instead.


Freshwater heliozoan feeding on small flagellated algae

Phylogeny

The heliozoa are a polyphyletic grouping of various protists that have independently evolved axopodial arms. Some of the heliozoan groups are intermingled in the supergroup Rhizaria with radiolarians, their mostly marine counterpart. [6]

Eukaryotes

Related Research Articles

<span class="mw-page-title-main">Actinophryid</span> Order of heliozoan protists

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 are unicellular and roughly spherical in shape, with many axopodia that radiate outward from the cell body. Axopodia are a type of pseudopodia that are supported by hundreds of microtubules arranged in interlocking spirals and forming a needle-like internal structure or axoneme. Small granules, extrusomes, that lie under the membrane of the body and axopodia capture flagellates, ciliates and small metazoa that make contact with the arms.

<span class="mw-page-title-main">Flagellate</span> Group of protists with at least one whip-like appendage

A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word flagellate also describes a particular construction characteristic of many prokaryotes and eukaryotes and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagella. However, several derivations of the term "flagellate" are more formally characterized.

The gymnosphaerids are a small group of heliozoan protists found in marine environments. They tend to be roughly spherical with radially directed axopods, supported by microtubules in a triangular-hexagonal array arising from an amorphous central granule.

<span class="mw-page-title-main">Centrohelid</span> Group of algae

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.

<span class="mw-page-title-main">Radiolaria</span> Phylum of single-celled organisms

The Radiolaria, also called Radiozoa, are protozoa of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ectoplasm. The elaborate mineral skeleton is usually made of silica. They are found as zooplankton throughout the global ocean. As zooplankton, radiolarians are primarily heterotrophic, but many have photosynthetic endosymbionts and are, therefore, considered mixotrophs. The skeletal remains of some types of radiolarians make up a large part of the cover of the ocean floor as siliceous ooze. Due to their rapid change as species and intricate skeletons, radiolarians represent an important diagnostic fossil found from the Cambrian onwards.

<span class="mw-page-title-main">Axodine</span> Class of single-celled organisms

The axodines are a group of unicellular stramenopiles that includes silicoflagellate and rhizochromulinid algae, actinomonad heterotrophic flagellates and actinophryid heliozoa. Alternative classifications treat the dictyochophytes as heterokont algae, or as Chrysophyceae. Other overlapping taxonomic concepts include the Actinochrysophyceae, Actinochrysea or Dictyochophyceae sensu lato. The grouping was proposed on the basis of ultrastructural similarities, and is consistent with subsequent molecular comparisons.

<span class="mw-page-title-main">Heliomonadida</span> Order of single-celled organisms

The Heliomonadida are a small group of heliozoan amoeboids that are unusual in possessing flagella throughout their life cycle.

<span class="mw-page-title-main">Thomas Cavalier-Smith</span> British evolutionary biologist (1942–2021)

Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow, was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford.

<span class="mw-page-title-main">Cercozoa</span> Group of single-celled organisms

Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eukaryotic group to be recognized mainly through molecular phylogenies. They are the natural predators of many species of bacteria. They are closely related to the phylum Retaria, comprising amoeboids that usually have complex shells, and together form a supergroup called Rhizaria.

<span class="mw-page-title-main">Rhizaria</span> Infrakingdom of protists

The Rhizaria are a diverse and species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthetic, but many foraminifera and radiolaria have a symbiotic relationship with unicellular algae. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has been described. This group was used by Cavalier-Smith in 2002, although the term "Rhizaria" had been long used for clades within the currently recognized taxon.

<span class="mw-page-title-main">Phaeodarea</span> Class of protists

Phaeodarea or Phaeodaria is a group of amoeboid cercozoan organisms. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa. They are distinguished by the structure of their central capsule and by the presence of a phaeodium, an aggregate of waste particles within the cell.

<span class="mw-page-title-main">Telonemia</span> Phylum of single-celled organisms

Telonemia is a phylum of microscopic eukaryotes commonly known as telonemids. They are unicellular free-living flagellates with a unique combination of cell structures, including a highly complex cytoskeleton unseen in other eukaryotes.

<span class="mw-page-title-main">Protist</span> Eukaryotes other than animals, plants or fungi

A protist or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a polyphyletic grouping of several independent clades that evolved from the last eukaryotic common ancestor.

<span class="mw-page-title-main">Protozoa</span> Single-celled eukaryotic organisms that feed on organic matter

Protozoa are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically, protozoans were regarded as "one-celled animals".

<span class="mw-page-title-main">Imbricatea</span> Class of single-celled organisms

Imbricatea is a class of Rhizaria characterised by silica scales. It is sometimes described as "Imbricatea/Silicofilosea", due to the similarity of those two groupings. Imbricatea is divided into the orders Euglyphida and Thaumatomonadida.

<span class="mw-page-title-main">Katablepharid</span> Group of algae

The kathablepharids or katablepharids are a group of heterotrophic flagellates closely related to cryptomonads. First described by Heinrich Leonhards Skuja in 1939, kathablepharids were named after the genus Kathablepharis. This genus is corrected to Katablepharis under botanical nomenclature, but the original spelling is maintained under zoological nomenclature. They are single-celled protists with two anteriorly directed flagella, an anterior cytostome for ingesting eukaryotic prey, and a sheath that covers the cell membrane. They have extrusomes known as ejectisomes, as well as tubular mitochondrial cristae.

Pinaciophora is an amoeboid genus of Heliozoa of uncertain affinity, previously classified as Rhizaria.

<span class="mw-page-title-main">Amoeba</span> Cellular body type

An amoeba, often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods. Amoebae do not form a single taxonomic group; instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa, but also in fungi, algae, and animals.

<span class="mw-page-title-main">Ultrastructural identity</span>

Ultrastructural identity is a concept in biology. It asserts that evolutionary lineages of eukaryotes in general and protists in particular can be distinguished by complements and arrangements of cellular organelles. These ultrastructural components can be visualized by electron microscopy.

Heliorapha is a genus of heliozoan protists, amoeboid eukaryotes with stiff axopodia radiating from their cells. It contains one species, Heliorapha azurina. It is classified within a monotypic family Helioraphidae inside the actinophryids, a group of heliozoa that belong to the Ochrophyta along with other protists such as diatoms and brown algae.

References

  1. Guiry, M.D. & Guiry, G.M. (2024). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway (taxonomic information republished from AlgaeBase with permission of M.D. Guiry). Heliozoa. Accessed through: World Register of Marine Species at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=341274 on 16 June 2024
  2. Cavalier-Smith T, von der Heyden S (September 2007). "Molecular phylogeny, scale evolution and taxonomy of centrohelid heliozoa". Mol. Phylogenet. Evol. 44 (3): 1186–203. Bibcode:2007MolPE..44.1186C. doi:10.1016/j.ympev.2007.04.019. PMID   17588778.
  3. "Sarcodia" . Retrieved 28 August 2014.
  4. D.J. Patterson (1996). Free-living freshwater Protozoa. ASM Press. p. 168.
  5. Cavalier-Smith, Thomas (December 1993). "Kingdom Protozoa and its 18 phyla". Microbiological Reviews. 57 (4): 953–994. doi:10.1128/mmbr.57.4.953-994.1993. PMC   372943 . PMID   8302218.
  6. 1 2 Nikolaev SI, Berney C, Fahrni JF, et al. (May 2004). "The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes". Proc. Natl. Acad. Sci. U.S.A. 101 (21): 8066–71. doi: 10.1073/pnas.0308602101 . PMC   419558 . PMID   15148395.
  7. Cavalier-Smith, Thomas; Chao, Ema E. (2012). "Oxnerella micra sp. n. (Oxnerellidae fam. n.), a Tiny Naked Centrohelid, and the Diversity and Evolution of Heliozoa". Protist. 163 (4): 574–601. doi:10.1016/j.protis.2011.12.005. PMID   22317961.