''Arcella'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

testate amoebae Testate amoebae (formerly thecamoebians, Testacea or Thecamoeba) are a polyphyletic group of unicellular amoeboid protists, which differ from naked amoebae in the presence of a test that partially encloses the cell, with an aperture from which th ...

in the order Arcellinida, usually found in

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 incl ...

s and

moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and ...

es, and rarely in soils. A key characteristic of ''Arcella'' is the circular

test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...

with a hole on its center from where finger-like pseudopods emerge. It is one of the largest testacean genera.

Anatomy

An ''Arcella'' is typically enclosed in a

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

ous, umbrella-shaped

(or shell) that has a single central aperture through which the

pseudopod 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 ...

s – which are used for locomotion – extend out. In some species the aperture is surrounded by a ring of pores. The test is composed of organic material with a diameter of up to 300 µm and is transparent or light-yellow-colored in young ''Arcella'', but browns while aging due to the progressive deposition of

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

and

manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...

compounds.Ralf Meisterfeld and Edward Mitchell (2008)
"''Arcella'' Ehrenberg 1832"
Contrary to other genera, no gravel chips or other foreign bodies are inserted to strengthen the housing. Different species of ''Arcella'' can have different number of nuclei, ranging from a single nucleus, as in some '' A. hemisphaerica'', up to 200 nuclei, as in '' A. megastoma'', though the majority is binucleate. They also have many

contractile vacuole A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists and in unicellular algae. It was previously known as pulsatile or pulsating vacuole. Overview The contractile va ...

s, and can develop vacuoles of carbon dioxide in their cytoplasm to float up to the surface of the water.

Nutrition and distribution

''Arcella'' inhabit

pools,

eutrophic Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplan ...

waters,

marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found ...

es,

es, as well as wet foliage. Few species can also be found in soils. They nourish on

diatom A diatom ( Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising se ...

s, unicellular

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/ Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga ...

or animal protozoa such as

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and thei ...

s and

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a differen ...

s. Most species are worldwide-distributed, but some have restricted distributions, e.g. ''A. brasiliensis'' and ''A. rota'' which are endemic to South America. They eat by stretching out their pseudopods to surround the food and bring it back to the microorganism.

Species

Over 130 species and subspecies of the genus ''Arcella'' have been described so far. Species include: *''

Arcella arenaria ''Arcella'' is a genus of testate amoebae in the order Arcellinida, usually found in freshwaters and mosses, and rarely in soils. A key characteristic of ''Arcella'' is the circular test with a hole on its center from where finger-like pseudopod ...

'' Greeff, 1866
Microworld Arcella *''

Arcella artocrea ''Arcella'' is a genus of testate amoebae in the order Arcellinida, usually found in freshwaters and mosses, and rarely in soils. A key characteristic of ''Arcella'' is the circular test with a hole on its center from where finger-like pseudopod ...

'' Leidy, 1876 *''

Arcella brasiliensis ''Arcella'' is a genus of testate amoebae in the order Arcellinida, usually found in freshwaters and mosses, and rarely in soils. A key characteristic of ''Arcella'' is the circular test with a hole on its center from where finger-like pseudopod ...

'' Cunha, 1913 *''

Arcella catinus ''Arcella'' is a genus of testate amoebae in the order Arcellinida, usually found in freshwaters and mosses, and rarely in soils. A key characteristic of ''Arcella'' is the circular test with a hole on its center from where finger-like pseudopod ...

'' Penard, 1890 *''

Arcella conica ''Arcella'' is a genus of testate amoebae in the order Arcellinida, usually found in freshwaters and mosses, and rarely in soils. A key characteristic of ''Arcella'' is the circular test with a hole on its center from where finger-like pseudopod ...

'' (Playfair, 1918) * ''

Arcella costata ''Arcella'' is a genus of testate amoebae in the order Arcellinida, usually found in freshwaters and mosses, and rarely in soils. A key characteristic of ''Arcella'' is the circular test with a hole on its center from where finger-like pseudopod ...

'' Ehrenberg, 1847 *'' Arcella dentata'' Ehrenberg, 1830 *'' Arcella discoides'' Ehrenberg, 1843 ** ''Arcella discoides var. scutelliformis'' Playfair, 1918 *'' Arcella excavata'' Cunningham, 1919
* Arcella gandalfi Féres et al., 2016 Microworld
/ref> *'' Arcella gibbosa'' Penard, 1890 *'' Arcella hemisphaerica'' Perty, 1852 * '' Arcella intermedia'' (Deflandre, 1928) Tsyganov & Mazei 2006 *''

Arcella megastoma ''Arcella'' is a genus of testate amoebae in the order Arcellinida, usually found in freshwaters and mosses, and rarely in soils. A key characteristic of ''Arcella'' is the circular test with a hole on its center from where finger-like pseudopod ...

'' Penard, 1902 * '' Arcella mitrata'' Leidy, 1876 * '' Arcella multilobata'' Golemansky, 1964 * '' Arcella ovaliformis'' Chardez and Beyens, 1987 * ''

Arcella rota ''Arcella'' is a genus of testate amoebae in the order Arcellinida, usually found in freshwaters and mosses, and rarely in soils. A key characteristic of ''Arcella'' is the circular test with a hole on its center from where finger-like pseudopod ...

'' Daday, 1905 *'' Arcella peruviana'' Reczuga et al., 2015 * '' Arcella rotundata'' Playfair, 1918 *'' Arcella vulgaris'' Ehrenberg, 1830

References

External links

{{Taxonbar, from=Q971534 Amoebozoa genera Tubulinea Taxa named by Christian Gottfried Ehrenberg