Arcella is a genus of testate amoebae in the order Arcellinida, commonly found in ponds, wetlands, moss, and soil. It is distinguished by a radially symmetrical organic shell, which features a central aperture through which pseudopods are extended. Recognized for its broad ecological adaptability, Arcella has been described as "probably the most ecologically successful Arcellinid taxon", with several species exhibiting a cosmopolitan distribution across diverse environments.
Description
Species of Arcella are typically enclosed in a domed or umbrella-shaped test (shell) with a single central aperture."Arcella Ehrenberg, 1832". National Institute for Environmental Studies, Japan. This test is composed of secreted proteinaceous material, arranged in hexagonal units known as "areoles." Unlike many other genera in the order Arcellinida, Arcella species do not incorporate scavenged materials, such as mineral particles or diatoms, in their shells. The shape of the shell varies from one species to the next, and sizes range from less than 50 μm to well over 300 μm. When newly-formed, Arcella tests are transparent or pale yellow in colour. As shells age, they gradually darken, becoming nearly brown due to the progressive deposition of iron and manganese compounds.Ralf Meisterfeld and Edward Mitchell (2008). "Arcella Ehrenberg 1832".
Most species of Arcella have two cell nuclei, but some are multinucleate. Cells do not entirely fill the test in which they live, but are connected to the inner surface by thin strands of cytoplasm known as epipodia.
Taxonomy The genus Arcella was established in 1830 by the German zoologist C. G. Ehrenberg, who designated Arcella vulgaris as the type species. Over time, numerous species were added to the genus, and by the early 21st century, approximately 51 nominal species, 71 varieties, and 27 distinct forms had been recognized.
In 2021, González-Miguéns et al. conducted a comprehensive revision of the family Arcellidae, using molecular phylogenetics to uncover evolutionary relationships within the group. Their findings led to the reclassification of six Arcella species, which were transferred to the newly established genus Galeripora. This genus was distinguished by the presence of pores surrounding the aperture of the test and a thin layer of organic material partially covering the shell's surface. Since then, several other species previously classified in Arcella have been transferred to Galeripora.
Species The genus Arcella includes the following species:
Arcella apicata Schaudinn, 1898 Arcella brasiliensis Cunha, 1913 Microworld Arcella Arcella conica (Playfair, 1918) Arcella corona Van Oye, 1926 Arcella costata Ehrenberg, 1847 Arcella crenata Playfair, 1917 Arcella crenulata Deflandre, 1928 Arcella euryhalina Useros et al., 2023 Arcella excavata Cunningham, 1919 Arcella formosa Nicholls, 2005 Arcella gandalfi Féres et al., 2016Newfound Amoeba Looks Just Like Gandalf the Wizard's HatMicroworld Arcella gibbosa Penard, 1890 Arcella grospietschi Stepanek, 1963 Arcella guadarramensis González-Miguéns & Lara, 202 Arcella hemisphaerica Perty, 1852 Arcella intermedia (Deflandre, 1928) Tsyganov & Mazei 2006 Arcella jeanneli Virieux, 1913 Arcella leidyana Deflandre, 1928 Arcella lichenophila Decloitre, 1965 Arcella lobostoma Deflandre, 1929 Arcella manipurensis Chattopadhyay & Das, 2003 Arcella marginata Daday, 1905 Arcella mitrata Leidy, 1876 Arcella mitriformis (Deflandre, 1928) Siemensma, 2025 Arcella multilobata Golemansky, 1964 Arcella nordestina Vucetich, 1973 Arcella oblonga Schaudinn, 1898 Arcella oyei Stepanek, 1963 Arcella peruviana Reczuga et al., 2015 Arcella prismatica Taylor, Strueder-Kypke and Siemensma Arcella rotundata Playfair, 1918 Arcella rukiensis Van Oye, 1926 Arcella salobris Useros et al., 2023 Arcella spectabilis (Deflandre, 1928) Siemensma, 2025 Arcella uspiensis Ribeiro, Porfírio- Sousa, Lahr & Lara, 2023 Arcella vulgaris Ehrenberg, 1830
Ecology Arcella inhabit a wide range of freshwater environments, including pools, eutrophic waters, marshes, mosses, slow-moving streams, and wet foliage. A few species can also be found in soils. While most species are associated with fresh water, some have been found in coastal salt marshes, and saline lakes.
Like other amoebae, Arcella use their pseudopods to take in food. They feed on bacteria, green algae, diatoms, fungi, flagellates and small ciliates.
Most species are cosmopolitan, meaning they occur worldwide. However, some species have more restricted distributions, such as A. brasiliensis, A. peruviana and A. gandalfi, which are endemic to South America.
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