Amoebozoa
Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classification schemes, Amoebozoa is ranked as a phylum within either the kingdom Protista or the kingdom Protozoa. In the classification favored by the International Society of Protistologists, it is retained as an unranked "supergroup" within Eukaryota. Molecular genetic analysis supports Amoebozoa as a monophyletic clade. Modern studies of eukaryotic phylogenetic trees identify it as the sister group to Opisthokonta, another major clade which contains both fungi and animals  as well as several other clades comprising some 300 species of unicellular eukaryotes. Amoebozoa and Opisthokonta are sometimes grouped together in a high-level taxon, variously named Unikonta, Amorphea or Opimoda. Amoebozoa includes many of the best-known amoeboid organisms, such as "Chaos", "Entamoeba", "Pelomyxa" and the genus "Amoeba" itself. Species of Amoebozoa may be either shelled (testate) or naked, and cells may possess flagella. Free-living species are common in both salt and freshwater as well as soil, moss and leaf litter. Some live as parasites or symbionts of other organisms, and some are known to cause disease in  humans and other organisms. While the majority of amoebozoan species are unicellular, the group also includes several clades of slime molds, which have a macroscopic, multicellular stage of life during which individual amoeboid cells remain together after multiple cell division to form a macroscopic plasmodium or, in cellular slime molds, aggregate to form one. Amoebozoa vary greatly in size. Some are only 10–20 μm in diameter, while others are among the largest protozoa. The well-known species "Amoeba proteus," which may reach 800 μm in length, is often studied in schools and laboratories as a representative cell or model organism , partly because of its convenient size. Multinucleate amoebae like "Chaos" and "Pelomyxa" may be several millimetres in length, and some multicellular amoebozoa, such as the "dog vomit" slime mold "Fuligo septica", can cover an area of several square meters. Morphology. Amoebozoa is a large and diverse group, but certain features are common to many of its members. The amoebozoan cell is typically divided into a granular central mass, called endoplasm, and a clear outer layer, called ectoplasm. During locomotion, the endoplasm flows forwards and the ectoplasm runs backwards along the outside of the cell. In motion, many amoebozoans have a  clearly defined anterior and posterior and may assume a "monopodial" form, with the entire cell functioning as a single pseudopod. Large pseudopods may produce numerous clear projections called subpseudopodia (or determinate pseudopodia), which are extended to a certain length and then retracted, either for the purpose of locomotion or food intake. A cell may also form multiple indeterminate pseudopodia, through which the entire contents of the cell flow in the direction of locomotion. These are more or less tubular and are mostly filled with granular endoplasm. The cell mass flows into a leading pseudopod, and the others ultimately retract, unless  the organism changes direction. While most amoebozoans are "naked," like the familiar "Amoeba" and "Chaos", or covered with a loose coat of minute scales, like Cochliopodium and Korotnevella, members of the order Arcellinida form rigid shells, or tests, equipped with a single aperture through which the pseudopods emerge. Arcellinid tests may be secreted from organic materials, as in "Arcella", or built up from collected particles cemented together, as in "Difflugia. " In all amoebozoa, the primary mode of nutrition is phagocytosis, in which the cell surrounds potential food particles with its pseudopods, sealing them into vacuoles within which they may be  digested and absorbed. Some amoebozoans have a posterior bulb called a uroid, which may serve to accumulate waste, periodically detaching from the rest of the cell. When food is scarce, most species can form cysts, which may be carried aerially and introduce them to new environments. In slime moulds, these structures are called spores, and form on stalked structures called fruiting bodies or sporangia. The majority of Amoebozoa lack flagella and more generally do not form microtubule-supported structures except during mitosis. However, flagella do occur among the Archamoebae, and many slime moulds produce biflagellate gametes . The flagellum is generally  anchored by a cone of microtubules, suggesting a close relationship to the opisthokonts. The mitochondria in amoebozoan cells characteristically have branching tubular cristae. However, among the Archamoebae, which are adapted to anoxic or microaerophilic habitats, mitochondria have been lost. Classification. Place of Amoebozoa in the eukaryote tree. It appears (based on molecular genetics) that the members of Amoebozoa form a sister group to animals and fungi, diverging from this lineage after it had split from the other groups, as illustrated below in a simplified diagram: Strong similarities between Amoebozoa and Opisthokonts lead to the hypothesis that they form a distinct  clade. Thomas Cavalier-Smith proposed the name "unikonts" (formally, Unikonta) for this branch, whose members were believed to have been descended from a common ancestor possessing a single emergent flagellum rooted in one basal body. However, while the close relationship between Amoebozoa and Opisthokonta is robustly supported, recent work has shown that the hypothesis of a uniciliate ancestor is probably false. In their Revised Classification of Eukaryotes (2012), Adl et al. proposed Amorphea as a more suitable name for a clade of approximately the same composition, a sister group to the Diaphoretickes. More recent work places the members of Amorphea  together with the malawimonids and collodictyonids in a proposed clade called Opimoda, which comprises one of two major lineages diverging at the root of the eukaryote tree of life, the other being Diphoda. Subphyla within Amoebozoa: Lobosa and Conosa. Traditionally all amoebozoa with lobose pseudopods were grouped together in the class Lobosea, placed with other amoeboids in the phylum Sarcodina or Rhizopoda, but these were considered to be unnatural groups. Structural and genetic studies identified the percolozoans and several archamoebae as independent groups. In phylogenies based on rRNA their representatives were separate from other amoebae, and appeared to diverge near  the base of eukaryotic evolution, as did most slime molds. However, revised trees by Cavalier-Smith and Chao in 1996 suggested that the remaining lobosans do form a monophyletic group, to which the Archamoebae and Mycetozoa were closely related, although the percolozoans were not. Subsequently, they emended the phylum Amoebozoa to include both the subphylum Lobosa and a new subphylum Conosa, comprising the Archamoebae and the Mycetozoa. Recent molecular genetic data appear to support this primary division of the Amoebozoa into Lobosa and Conosa. The former, as defined by Cavalier-Smith and his collaborators, consists largely of the classic Lobosea : non-flagellated amoebae with blunt, lobose pseudopods ("Amoeba", "Acanthamoeba, Arcella, Difflugia etc."). The latter is made up of both amoeboid and flagellated cells, characteristically with more pointed or slightly branching subpseudopodia (Archamoebae and the Mycetozoan slime molds). Phylogeny and taxonomy within Amoebozoa. From older studies by Cavalier-Smith, Chao & Lewis 2016 and Silar 2016. Also recent phylogeny indicates the Lobosa are paraphyletic: Conosa is sister of the Cutosea. Phylum Amoebozoa [Amoebobiota; Eumycetozoa ] Fossil record. Vase-shaped microfossils (VSMs) discovered around the world show that amoebozoans have existed since the Neoproterozoic Era. The fossil species "Melanocyrillium hexodiadema", "Palaeoarcella athanata", and "Hemisphaeriella  ornata" come from rocks 750 million years old. All three VSMs share a hemispherical shape, invaginated aperture, and regular indentations, that strongly resemble modern arcellinids, which are shell-bearing amoeboids. "P. athanata" in particular looks the same as the extant genus "Arcella". Meiosis. The recently available "Acanthamoeba" genome sequence revealed several orthologs of genes employed in meiosis of sexual eukaryotes. These genes included "Spo11, Mre11, Rad50, Rad51, Rad52, Mnd1, Dmc1, Msh" and "Mlh". This finding suggests that "Acanthamoeba" is capable of some form of meiosis and may be able to undergo sexual reproduction. In sexually reproducing eukaryotes, homologous recombination (HR ) ordinarily occurs during meiosis. The meiosis-specific recombinase, Dmc1, is required for efficient meiotic HR, and Dmc1 is expressed in "Entamoeba histolytica". The purified Dmc1 from "E. histolytica" forms presynaptic filaments and catalyzes ATP-dependent homologous DNA pairing and DNA strand exchange over at least several thousand base pairs. The DNA pairing and strand exchange reactions are enhanced by the eukaryotic meiosis-specific recombination accessory factor (heterodimer) Hop2-Mnd1. These processes are central to meiotic recombination, suggesting that "E. histolytica" undergoes meiosis. Studies of "Entamoeba invadens" found that, during the conversion from the tetraploid uninucleate trophozoite to the tetranucleate cyst , homologous recombination is enhanced. Expression of genes with functions related to the major steps of meiotic recombination also increased during encystations. These findings in "E. invadens", combined with evidence from studies of "E. histolytica" indicate the presence of meiosis in the "Entamoeba". A comparative genetic analysis indicated that meiotic processes are present in all major amoebozoan lineages. Since "Amoebozoa" diverged early from the eukaryotic family tree, these results also suggest that meiosis was present early in eukaryotic evolution. Human health. Amoebiasis, also known as amebiasis or entamoebiasis, is an infection caused by any of the amoebozoans of the "Entamoeba" group . Symptoms are most common upon infection by "Entamoeba histolytica". Amoebiasis can present with no, mild, or severe symptoms. Symptoms may include abdominal pain, mild diarrhoea, bloody diarrhea or severe colitis with tissue death and perforation. This last complication may cause peritonitis. People affected may develop anemia due to loss of blood. Invasion of the intestinal lining causes amoebic bloody diarrhea or amoebic colitis. If the parasite reaches the bloodstream it can spread through the body, most frequently ending up in the liver where it causes amoebic liver abscesses. Liver abscesses can occur without previous diarrhea. Cysts of "Entamoeba" can survive  for up to a month in soil or for up to 45 minutes under fingernails. It is important to differentiate between amoebiasis and bacterial colitis. The preferred diagnostic method is through faecal examination under microscope, but requires a skilled microscopist and may not be reliable when excluding infection. This method however may not be able to separate between specific types. Increased white blood cell count is present in severe cases, but not in mild ones. The most accurate test is for antibodies in the blood, but it may remain positive following treatment. Prevention of amoebiasis is by separating food and  water from faeces and by proper sanitation measures. There is no vaccine. There are two treatment options depending on the location of the infection. Amoebiasis in tissues is treated with either metronidazole, tinidazole, nitazoxanide, dehydroemetine or chloroquine, while luminal infection is treated with diloxanide furoate or iodoquinoline. For treatment to be effective against all stages of the amoeba may require a combination of medications. Infections without symptoms do not require treatment but infected individuals can spread the parasite to others and treatment can be considered. Treatment of other "Entamoeba" infections apart from "E. histolytica" is not needed. Amoebiasis is present  all over the world. About 480 million people are infected with what appears to be "E. histolytica" and these result in the death of between 40,000–110,000 people every year. Most infections are now ascribed to "E. dispar". "E. dispar" is more common in certain areas and symptomatic cases may be fewer than previously reported. The first case of amoebiasis was documented in 1875 and in 1891 the disease was described in detail, resulting in the terms "amoebic dysentery" and "amoebic liver abscess". Further evidence from the Philippines in 1913 found that upon ingesting cysts of "E. histolytica" volunteers developed the  disease. It has been known since 1897 that at least one non-disease-causing species of "Entamoeba" existed ("Entamoeba coli"), but it was first formally recognized by the WHO in 1997 that "E. histolytica" was two species, despite this having first been proposed in 1925. In addition to the now-recognized "E. dispar" evidence shows there are at least two other species of "Entamoeba" that look the same in humans - "E. moshkovskii" and "Entamoeba bangladeshi". The reason these species haven't been differentiated until recently is because of the reliance on appearance.