Phylum Foraminifera d’Orbigny, 1826
Foraminifera are typically deﬁned as unicellular organisms characterized by the presence of granuloreticulopodia. Some species are naked, but most have a membranous, agglutinated, or calcareous test, which is either monothalamous (single-chambered) or polythalamous (multi-chambered). Foraminifera live in marine and brackish habitats, but some members of this phylum can be found in freshwater, where they live between submerged mosses, in sediment, and also in mosses growing on soil, trees and walls.
Non-marine foraminifera are among the least known groups of protists and only a handful of species have been described since the 19th century. These non-marine species seem to be rare, only a handful of people ever found them, despite of their relatively large size. All known freshwater and soil species are monothalamous, and therefore called monothalamids or traditionally ‘allogromids’, and now defined as foraminifera that are either naked or possess a monothalamous test. This test can be organic-walled or embedded with agglutinated particles gathered from the surrounding sediment. These three morphotypes are respectively called naked, organic-walled and agglutinated monothalamids, an artificial classification that has no phylogenetical base, because many monothalamid clades comprise both organic-walled and agglutinated species.