Difflugia
Difflugia is the largest genus of Arcellinida, one of several groups of Tubulinea within the eukaryote supergroup Amoebozoa. Arcellinida species produce shells or tests from mineral particles or biogeonic elements (e.g. diatom frustules) and are thus commonly referred to as testate amoebae or shelled amoebae. "Difflugia" are particularly common in marshes and other freshwater habitats. History. The genus "Difflugia" was initially discovered in 1815 by L, Leclerc, but its infra-generic classification as a group is still unclear. The genus "Difflugia" is the oldest and most diverse of the testate amoebae. It contains more than 300 species and countless  subspecies since even minor differences in morphology result in classification as a new species. In 1958, Gauthier-Lièvre and Thomas divided the genus into 10 groups depending on difference in shell morphology. These 10 groups are based on a survey conducted of the African species of "Difflugia" The 10 shell shape classifications are lobed, collared, compressed, urceolate, globose, ovoid-globose, elongate, acute angled, horned and pyriform. Taxonomy. There have been issues coming to a specific consensus about the taxonomy of the genus "Difflugia". In 1988, an attempt to characterize and create a phylogenetic tree based upon the composition of the  shell. However, with additional evidence it was found that this is not actually a useful characteristic to evaluate by. In addition, most initial descriptions of "Difflugia" speciation were completed using light microscopy and therefore lacked the technology to show the details of test structure and composition. The invention of scanning electron microscopy allows for more detail and improved the taxonomic work surrounding "Difflugia". Studies surrounding "Difflugia" have been centered around species found mostly in Europe and Africa. Molecular phylogenetic analyses have revealed that the genus "Difflugia", as traditionally defined, is not a monophyletic group. As a result, several globular and  oviform species have been transferred to the genus "Netzelia". Structure. "Difflugia" are testate amoebae with an agglutinate shell. The test can be composed of various different mineral particles depending on the varying environment. These mineral particles are collectively called xenosomes. All species of the genus "Difflugia" acquire their xenosomes, from the environment in which they inhabit. "Difflugia" often have species specific tests, which are arranged based on the specific shape and size. Most species of "Difflugia" only contain one nucleus but there are a select few that are multinucleated. In the larger species the nucleus can be vesicular as opposed  to the regularly ovular nucleus. All species also contain an epipodium which is a terminal aperture in the protist's structure. The size of "Difflugia" is found to range from 15μm all the way up to 500μm. During cell division, the particles collected that have been used to produce the test are directly passed on to the daughter cell. Strength of the test is quite variable between the "Difflugia" species and the strength of the test can be separated into three categories; robust, intermediate and fragile. Robust tests are found to result in a shell with an irregular shape in  comparison to the rest of the genus. Shells which are a part of the fragile category are most likely to be constructed from diatom crystals. Habitat and ecology. The environment conditions in which "Difflugia" lives is important to consider as it greatly influences shell morphology of the species. Shell composition depends on environmental pH and what materials are available. "Difflugia" can be found living in a large variety of habitats such as freshwater sediments, dry mosses and soil, or lakes. Some species are planktonic and switch to a benthic phase during the winter in which they stay immobile near the  bottom of the body of water. One way environment can influence characteristics of "Difflugia" is that there are several freshwater species, which have green endosymbionts or zoochlorellae. The species "Difflugia" that contain endosymbionts are not considered to be heterotrophs, but instead mixotrophs because they combine being autotrophic and heterotrophic. The source of food depends on the environment but across the genus it is found to be mainly algae and fungi. Smaller species of "Difflugia" are found to consume bacteria as well as algae and fungi. Fossil history. The presence of a test in "Difflugia" allowed them to be extremely well -preserved in fossils. "Difflugia" are part of one of the oldest lineages of eukaryotes based on fossile records which date back 750Mya. The only structure of the organisms that was able to be preserved in the fossils was the test. Therefore there have been issues differentiating genera such as "Cryptodifflugia" from "Difflugia" based on fossil record alone. Another problem arise from the distortion of test and changes to the xenosomes that makes genera difficult to identify from the testate amoebae fossil specimen alone.