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Arcellinida

Order of Amoebozoa

Wikipedia contributorsAdapted for Fathomly · View authors
4 min read
Source updated August 10, 2026
Image credit is listed at the end of this article.

Arcellinid testate amoebae or Arcellinida, Arcellacean or lobose testate amoebae are single-celled protists partially enclosed in a simple test (shell).

Arcellinid testate amoebae are commonly found in soils, leaf litter, peat bogs and near/in fresh water. They use their pseudopodia, a temporary cell extension, for moving and taking in food. Like most amoebae, they are generally believed to reproduce asexually via binary fission. However a recent review suggests that sexual recombination may be the rule rather than the exception in amoeboid protists in general, including the Arcellinid testate amoebae.

01Morphology

Arcellinida always have a shell or test. The tests lie outside the cell membrane and consist of organic or mineral materials that are either secreted or incorporate external particles. The test has a single main opening.

Simple tests are made by secretion (autogenous tests), agglutination of foreign material (xenogenous tests), or sometimes a combination of both. Past environmental changes can be determined by analysing the composition of fossil tests, including the reconstruction of past climate change. Testate amoebae species have been used to reconstruct hydrological changes over the late Holocene, as a result of individual species possessing a narrow tolerance for ecohydrological conditions such as water-table depth or pH.

Representation of an arcellinid Test, cemented sand, diatom frustules Contractile vacuole, regulates the quantity of water inside a cell Mitochondrion; creates ATP (energy) for the cell (flat cristae) Nucleolus Golgi apparatus, packages proteins Endoplasmic reticulum, the transport network for molecules going to specific parts of the cell Digestive Vacuole Lysosome, holds enzymes Phagosome, vesicle formed around a particle (prey not to scale) Xenosome, bacterium living inside cytoplasm Vesicles Lobopodia, a pseudopod or arm-like projection made of cytoplasm Prey (not to scale)
Representation of an arcellinid Test, cemented sand, diatom frustules Contractile vacuole, regulates the quantity of water inside a cell Mitochondrion; creates ATP (energy) for the cell (flat cristae) Nucleolus Golgi apparatus, packages proteins Endoplasmic reticulum, the transport network for molecules going to specific parts of the cell Digestive Vacuole Lysosome, holds enzymes Phagosome, vesicle formed around a particle (prey not to scale) Xenosome, bacterium living inside cytoplasm Vesicles Lobopodia, a pseudopod or arm-like projection made of cytoplasm Prey (not to scale)

02Evolutionary history

Fossils of arcellinid testate amoebae date back to the Tonian stage of the Proterozoic, around 789-759 million years ago. The fossils indicate that by 730 million years ago, arcellinids had already diversified into major lineages.

Testate amoebae are theorized to be mostly polyphyletic (coming from more than one ancestral type), but testaceafilosea, one group of testate amoebae, are theorized to be monophyletic. Ancient tests of terrestrial fauna are commonly found in fossilized amber, although mid-Cretaceous testate amoeba (i.e., Difflugia, Cucurbitella) have been found in ancient lake sediments. It is likely that the group has evolved minimally over the course of the Phanerozoic.

03Classification

Phylogeny of Arcellinida in 2019
Arcellinida

Phryganellina

Organoconcha

Glutinoconcha

Volnustoma

Hyalospheniformes

Excentrostoma

Sphaerothecina

Longithecina

Phylogeny of Arcellinida in 2022
Arcellinida

Phryganellina

Organoconcha

Glutinoconcha

Volnustoma

Hyalospheniformes

Excentrosoma

Cylindrothecina

Longithecina

Sphaerothecina

The classification of Arcellinida, as of 2019:

Arcellinida incertae sedis:

Watch videos about ArcellinidaExplainers and documentaries on YouTube (opens in a new tab)

Sources and credits

This article is adapted from the Wikipedia article “Arcellinida”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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