Order Arcellinida Kent 1880
Diagnosis: Cell enclosed in a hard or highly rigid extracellular test, composed of either self‑secreted elements (calcareous, siliceous, or chitinoid), a sheet‑like chitinoid structure, or recycled organic or mineral particles bound together. The test bears a single main aperture.
Remarks: Arcellinida comprises all testate amoebae with lobose pseudopodia. It is the largest group of testate amoebae, with 687 nominal species (Kosakyan et al., 2016). However, the majority of these species require comprehensive nomenclatural and taxonomic revision.
Members of Arcellinida exhibit a wide diversity of test shapes and compositions, which historically formed the basis for their classification. Meisterfeld (2000) divided the group into three suborders: Arcellina, Difflugina, and Phryganellina.
Recent molecular investigations have challenged this system, leading to the reassignment of many species and genera across families. These reconstructions have highlighted the limitations of test composition as a primary taxonomic character. Numerous revisions have been proposed at both higher and lower taxonomic levels. While the higher‑level taxonomy of Arcellinida remains uncertain, the lower‑level taxonomy is in constant flux (Kosakyan et al., 2016; Gomaa et al., 2017).
Further reading:
- Kosakyan et al. (2016): Current and future perspectives on the systematics, taxonomy and nomenclature of testate amoebae. European Journal of Protistology.
- Gomaa et al. (2017): A contribution to the phylogeny of agglutinating Arcellinida (Amoebozoa) based on SSU rRNA gene sequences. European Journal of Protistology 59: 99–107.
- González‑Miguéns et al. (2022): Deconstructing Difflugia: the tangled evolution of lobose testate amoebae shells (Amoebozoa: Arcellinida) illustrates the importance of convergent evolution in protist phylogeny. Molecular Phylogenetics and Evolution, doi: https://doi.org/10.1016/j.ympev.2022.107557
