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Wikipedia / Arcellinida

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.

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 (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.

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 (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.

Classification

The classification of Arcellinida, as of 2019:

Suborder Phryganellina Bovee 1985

Family Phryganellidae Jung 1942

Family Cryptodifflugiidae Jung 1942

Suborder Organoconcha Lahr et al. 2019

Family Microchlamyiidae Ogden 1985

Suborder Glutinoconcha Lahr et al. 2019

Infraorder Volnustoma Lahr et al. 2019

Family Heleoperidae Jung 1942

Infraorder Hyalospheniformes Lahr et al. 2019

Family Hyalospheniidae Schulze, 1977 [Nebelidae Taranek 1882]

Infraorder Excentrostoma Lahr et al. 2019

Family Centropyxidae

Family Plagiopyxidae

Infraorder Longithecina Lahr et al. 2019

Family Lesquereusiidae [Paraquadrulidae Deflandre 1953]

Family Difflugiidae Wallich 1864

Infraorder Sphaerothecina Kosakyan et al. 2016

Family Distomatopyxidae Bonnet 1970

Family Lamtopyxidae Bonnet 1974

Family Netzeliidae Kosakyan et al. 2016 [Cyclopyxidae Schönborn 1989]

Family Arcellidae Ehrenberg 1832

Trigonopyxidae Loeblich 1964

Arcellinida incertae sedis:

Family Bipseudostomatidae Snegovaya & Alekperov 2005

Family Mississippiellidae Huddleston & Haman 1985

Family Shamkiriidae Snegovaya & Alekperov 2005

References