Order Arcellinida Saville Kent 1880 (= Testacealobosia De Saedeleer 1934)
Diagnosis: Testate, inside an organic or mineral extracellular test of either self-secreted elements (calcareous, siliceous, or chitinoid) or recycled mineral particles bound together, with a single main opening.
Remarks: Arcellinida comprises all testate amoebae with lobose pseudopods. It is the largest group of testate amoebae with 687 nominal species (Kosakyan et al, 2016). However, the major part of these species needs comprehensive nomenclature and taxonomic revision.
Arcellinida exhibit a wide array of the test shapes composed of different material, which was the key characteristic for their classification. Meisterfeld (2000) organized them into three suborders: Arcellina, Difflugina and Phryganellina.
Recent molecular investigations has challenged the system, and the positions of many species and genera were switched between families. These molecular reconstructions have demonstrated the limitations of the use of test composition as a classification character. A number of modifications were made on high as well as low-taxonomic levels. Higher-level taxonomy of Arcellinida is uncertain, while lower-level taxonomy is constantly changing (Kosakyan et al, 2016).
Further reading: Kosakyan et al: Current and future perspectives on the systematics, taxonomy and nomenclature of testate amoebae - European Journal of Protistology, 2016.