''Arcella'' is a genus of

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 the ...

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 include ...

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 hor ...

es, and rarely in soils. A key characteristic of ''Arcella'' is the circular test 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 test (or shell) that has a single central aperture through which the pseudopods – 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 and manganese 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 vacuoles, 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 waters, marshes,

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 sev ...

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 as ...

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 their ...

s and ciliates. 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'' Greeff, 1866
Microworld Arcella *'' Arcella artocrea'' Leidy, 1876 *'' Arcella brasiliensis'' Cunha, 1913 *'' Arcella catinus'' Penard, 1890 *'' Arcella conica'' (Playfair, 1918) * '' Arcella costata'' Ehrenberg, 1847 *''

Arcella dentata ''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 (biology), test with a hole on its center from where finge ...

'' Ehrenberg, 1830 *''

Arcella discoides ''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, 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 ''Arcella hemisphaerica'' is an amoeboid An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, pr ...

'' Perty, 1852 * '' Arcella intermedia'' (Deflandre, 1928) Tsyganov & Mazei 2006 *'' Arcella megastoma'' Penard, 1902 * '' Arcella mitrata'' Leidy, 1876 * ''

Arcella multilobata ''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 ...

'' Golemansky, 1964 * '' Arcella ovaliformis'' Chardez and Beyens, 1987 * '' Arcella rota'' 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