Arcellinida


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

Morphology

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, agglutination of foreign material, 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.

Evolutionary 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, 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 have been found in ancient lake sediments. It is likely that the group has evolved minimally over the course of the Phanerozoic.

Classification

The classification of Arcellinida, as of 2019:
Arcellinida incertae sedis:Argynnia Vucetich, 1974Awerintzewia Schouteden, 1906Geamphorella Bonnet, 1959Jungia Loeblich & Tappan 1961Lagenodifflugia Medioli & Scott, 1983Lamtoquadrula Bonnet 1975Leptochlamys West 1901Maghrebia Gauthier-Lievre & Thomas, 1960Ochros Medioli et al. 1990
  • †Palaeoleptochlamys Strullu-Derrien et al. 2019Physochila Jung 1942Pseudawerintzewia Bonnet 1959Sacculus Medioli et al. 1990 non Gosse 1851 non Hirase 1927 non Neviani 1930Schoenbornia Decloitre 1964Swabia
  • Family Bipseudostomatidae Snegovaya & Alekperov 2005
  • * Bipseudostomatella Snegovaya & Alekperov 2005
  • * Gomocollariella Snegovaya & Alekperov 2005
  • Family Mississippiellidae Huddleston & Haman 1985
  • * Mississippiella Haman 1982
  • Family Shamkiriidae Snegovaya & Alekperov 2005
  • * Shamkiriella Snegovaya & Alekperov 2005