The Family Arcellidae is a group of unicellular organisms that belong to the phylum Amoebozoa. These organisms are commonly called Arcellids or Testate Amoebae. They are characterized by having a shell or test that is made up of organic matter and sand grains. This test is used for protection, as well as for locomotion and feeding. Other synonyms for the Family Arcellidae include the Arcellaceae, Arcellinidae, Testaceafilosia, and Testacealogia. These organisms can be found in freshwater environments and play an important role in nutrient cycling and ecological processes. Because of their unique morphology, they have attracted the attention of researchers studying bioindicators and paleoecology.