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Description of Arcella

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Testate amoebae Species with a more or less circular shell, aperture central, invaginated, in many species surrounded by a tubus or a circle of pores. Test completely organic, composed of box-like building units arranged in a single layer and cemented together resulting in an areolar surface. Size of the building units varies between species. Young shells are colourless, older cells become brown due to iron and manganese storage into the building units. Most species are binucleate, but several species have more; A. megastoma may have up to 200. These nuclei are always vesicular. Several contractile vacuoles. Cell does not fill the test, fixed with small pseudopodia at the shell wall. Lobose pseudopodia emerge from the aperture. Cyst: round, within test. About 50 species and many more varieties and forms. Type species: A. vulgaris Ehrenberg, 1832. Deflandre (1928) in his monograph has subdivided this genus in four artificial sections and four derived groups on the basis of the height/diameter ratio, the presence of angular facets or a flat circular rim.
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Arcella

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Arcella species

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 pseudopods emerge. It is one of the largest testacean genera.

Anatomy

An Arcella is typically enclosed in a chitinous, umbrella-shaped test (or shell) that has a single central aperture through which the pseudopods – which are used for locomotion – extend out.[1] 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.[2] 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.[2] 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 freshwater pools, eutrophic waters, marshes, mosses, as well as wet foliage. Few species can also be found in soils. They nourish on diatoms, unicellular green algae or animal protozoa such as flagellates 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 till now. Species include:

References

  1. ^ "Arcella Ehrenberg, 1832". National Institute for Environmental Studies, Japan.
  2. ^ a b Ralf Meisterfeld and Edward Mitchell (2008). "Arcella Ehrenberg 1832".
  3. ^ Microworld Arcella arenaria
  4. ^ a b c d e f g h i j k l m n o p q r s t [1] Microworld Arcella
  5. ^ Newfound Amoeba Looks Just Like Gandalf the Wizard's Hat
  6. ^ Microworld

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Arcella: Brief Summary

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 src= Arcella species

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 pseudopods emerge. It is one of the largest testacean genera.

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