42-441: Copromyxa is a genus of Amoebozoa in the Lobosa lineage of the eukaryotic supergroup Amoebozoa. It currently includes 2 species, the sorocarpic (aggregatively fruiting) amoeba Copromyxa protea and the non-sorocarpic amoeba Copromyxa (=Hartmannella) cantabrigiensis . The named species Copromyxa arborescens, is a synonym of C. protea . This Amoebozoa -related article
84-410: 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
126-512: A high-level taxon , named Amorphea . 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
168-509: 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 . Traditionally all amoebozoa with lobose pseudopods were grouped together in
210-424: A mouth or cytostome , and there is no fixed place on the cell at which phagocytosis normally occurs. Some amoebae also feed by pinocytosis , imbibing dissolved nutrients through vesicles formed within the cell membrane. The size of amoeboid cells and species is extremely variable. The marine amoeboid Massisteria voersi is just 2.3 to 3 micrometres in diameter, within the size range of many bacteria. At
252-400: 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 . Mixotrophic species living in
294-513: A secondary loss of the amoeboid phase. In his scheme, the Sarcodina were divided into the more primitive Eosarcodina (with the phyla Reticulosa and Mycetozoa) and the more derived Neosarcodina (with the phyla Amoebozoa for lobose amoebae and Rhizopoda for filose amoebae). Shortly after, phylogenetic analyses disproved this hypothesis, as non-amoeboid zooflagellates and amoeboflagellates were found to be completely intermingled with amoebae. With
336-428: A series of molecular phylogenetic analyses confirmed that Sarcodina was not a monophyletic group, and that amoebae evolved from flagellate ancestors. The protozoologist Thomas Cavalier-Smith proposed that the ancestor of most eukaryotes was an amoeboflagellate much like modern heteroloboseans , which in turn gave rise to a paraphyletic Sarcodina from which other groups (e.g., alveolates, animals, plants) evolved by
378-531: A symbiotic relationship with microalgae of the genus Chlorella , which lives inside the cytoplasm of their host, have been found in Arcellinida and Mayorella . 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
420-407: Is a stub . You can help Misplaced Pages by expanding it . 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 classification schemes, Amoebozoa is usually ranked as a phylum within either the kingdom Protista or
462-423: 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
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#1732876471155504-558: Is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods . Amoebae do not form a single taxonomic group ; instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa , but also in fungi , algae , and animals . Microbiologists often use the terms "amoeboid" and "amoeba" interchangeably for any organism that exhibits amoeboid movement . In older classification systems, most amoebae were placed in
546-486: 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. 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
588-675: Is transferred across the amoeba's cell membrane by osmosis . Without a contractile vacuole, the cell would fill with excess water and, eventually, burst. Marine amoebae do not usually possess a contractile vacuole because the concentration of solutes within the cell are in balance with the tonicity of the surrounding water. The food sources of amoebae vary. Some amoebae are predatory and live by consuming bacteria and other protists . Some are detritivores and eat dead organic material. Amoebae typically ingest their food by phagocytosis , extending pseudopods to encircle and engulf live prey or particles of scavenged material. Amoeboid cells do not have
630-787: The Acanthamoeba genome . These genes included Spo11 , Mre11 , Rad50 , Rad51 , Rad52 , Mnd1, Dmc1 , Msh and Mlh . This finding suggests that the ‘'Acanthamoeba'’ are capable of some form of meiosis and may be able to undergo sexual reproduction. The meiosis-specific recombinase , Dmc1 , is required for efficient meiotic homologous recombination , and Dmc1 is expressed in Entamoeba histolytica . The purified Dmc1 from E. histolytica forms presynaptic filaments and catalyses 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
672-516: The Radiolaria and Heliozoa , have stiff, needle-like, radiating axopodia (actinopoda) supported from within by bundles of microtubules . Free-living amoebae may be " testate " (enclosed within a hard shell), or "naked" (also known as gymnamoebae , lacking any hard covering). The shells of testate amoebae may be composed of various substances, including calcium , silica , chitin , or agglutinations of found materials like small grains of sand and
714-559: The class or subphylum Sarcodina, a grouping of single-celled organisms that possess pseudopods or move by protoplasmic flow. However, molecular phylogenetic studies have shown that Sarcodina is not a monophyletic group whose members share common descent . Consequently, amoeboid organisms are no longer classified together in one group. The best known amoeboid protists are Chaos carolinense and Amoeba proteus , both of which have been widely cultivated and studied in classrooms and laboratories. Other well known species include
756-817: The eukaryotic family tree, these results suggest that meiosis was present early in eukaryotic evolution. Furthermore, these findings are consistent with the proposal of Lahr et al. that the majority of amoeboid lineages are anciently sexual. Some amoebae can infect other organisms pathogenically , causing disease: Amoeba have been found to harvest and grow the bacteria implicated in plague . Amoebae can likewise play host to microscopic organisms that are pathogenic to people and help in spreading such microbes. Bacterial pathogens (for example, Legionella ) can oppose absorption of food when devoured by amoebae. The currently generally utilized and best-explored amoebae that host other organisms are Acanthamoeba castellanii and Dictyostelium discoideum. Microorganisms that can overcome
798-406: The frustules of diatoms . To regulate osmotic pressure , most freshwater amoebae have a contractile vacuole which expels excess water from the cell. This organelle is necessary because freshwater has a lower concentration of solutes (such as salt) than the amoeba's own internal fluids ( cytosol ). Because the surrounding water is hypotonic with respect to the contents of the cell, water
840-567: The plasma membrane that surrounds the cell. The appearance and internal structure of pseudopods are used to distinguish groups of amoebae from one another. Amoebozoan species, such as those in the genus Amoeba , typically have bulbous (lobose) pseudopods, rounded at the ends and roughly tubular in cross-section. Cercozoan amoeboids, such as Euglypha and Gromia , have slender, thread-like (filose) pseudopods. Foraminifera emit fine, branching pseudopods that merge with one another to form net-like (reticulose) structures. Some groups, such as
882-529: The 20th century. For convenience, all amoebae were grouped as Sarcodina and generally divided into morphological categories , on the basis of the form and structure of their pseudopods . Amoebae with pseudopods supported by regular arrays of microtubules (such as the freshwater Heliozoa and marine Radiolaria ) were classified as Actinopoda , whereas those with unsupported pseudopods were classified as Rhizopoda . The Rhizopods were further subdivided into lobose, filose, plasmodial and reticulose, according to
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#1732876471155924-450: The Austrian zoologist Ludwig Karl Schmarda used "sarcode" as the conceptual basis for his division Sarcodea, a phylum -level group made up of "unstable, changeable" organisms with bodies largely composed of "sarcode". Later workers, including the influential taxonomist Otto Bütschli , amended this group to create the class Sarcodina, a taxon that remained in wide use throughout most of
966-889: The Lobosa are paraphyletic: Conosa is sister of the Cutosea. Centramoebida Himatismenida Himatismenida Thecamoebida Dermamoebida Vannellida Dactylopodida Trichosida Microcoryciidae Echinamoebida Leptomyxida Euamoebida Arcellinida Squamocutida Entamoebida Pelobiontida Phalansteriida Flamellidae Ramamoebida Profiliida Fractovitellida Acytosteliales Dictyosteliida Ceratiomyxida Protosporangiida Cribrariales Reticulariales Liceida Trichiida Amoeba An amoeba ( / ə ˈ m iː b ə / ; less commonly spelled ameba or amœba ; pl. : amoebas (less commonly, amebas ) or amoebae ( amebae ) / ə ˈ m iː b i / ), often called an amoeboid ,
1008-671: The addition of many flagellates to Rhizopoda and the removal of some amoebae, the name was rejected in favour of a new name Cercozoa . As such, both names Rhizopoda and Sarcodina were finally abandoned as formal taxa, but they remained useful as descriptive terms for amoebae. The phylum Amoebozoa was conserved, as it still primarily included amoeboid organisms, and now included the Mycetozoa. Today, amoebae are dispersed among many high-level taxonomic groups. The majority of traditional sarcodines are placed in two eukaryote supergroups : Amoebozoa and Rhizaria . The rest have been distributed among
1050-502: 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
1092-475: 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). From older studies by Cavalier-Smith, Chao & Lewis 2016 and Silar 2016. Also recent phylogeny indicates
1134-560: The common species now known as Amoeba proteus . The term "Proteus animalcule" remained in use throughout the 18th and 19th centuries, as an informal name for any large, free-living amoeboid. In 1822, the genus Amiba (from the Greek ἀμοιβή amoibe , meaning "change") was erected by the French naturalist Bory de Saint-Vincent . Bory's contemporary, C. G. Ehrenberg , adopted the genus in his own classification of microscopic creatures, but changed
1176-471: The defenses of one-celled organisms can shelter and multiply inside them, where they are shielded from unfriendly outside conditions by their hosts. The earliest record of an amoeboid organism was produced in 1755 by August Johann Rösel von Rosenhof , who named his discovery "Der Kleine Proteus" ("the Little Proteus"). Rösel's illustrations show an unidentifiable freshwater amoeba, similar in appearance to
1218-406: 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
1260-430: 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
1302-674: 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
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1344-464: 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. Amoebozoa
1386-510: The major steps of meiotic recombination also increase during encystations. These findings in E. invadens , combined with evidence from studies of E. histolytica indicate the presence of meiosis in the Entamoeba . Dictyostelium discoideum in the supergroup Amoebozoa can undergo mating and sexual reproduction including meiosis when food is scarce. Since the Amoebozoa diverged early from
1428-424: 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
1470-407: The morphology of their pseudopods. During the 1980s, taxonomists reached the following classification, based exclusively on morphological comparisons: Archezoa Percolozoa (Heterolobosea) other excavates Eosarcodina Neosarcodina Apusozoa → Choanozoa → Animals , Fungi Actinopoda Alveolata → Plants , Chromista In the final decades of the 20th century,
1512-468: 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
1554-619: 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
1596-540: The other extreme, the shells of deep-sea xenophyophores can attain 20 cm in diameter. Most of the free-living freshwater amoebae commonly found in pond water , ditches, and lakes are microscopic , but some species, such as the so-called "giant amoebae" Pelomyxa palustris and Chaos carolinense , can be large enough to see with the naked eye. Recent evidence indicates that several Amoebozoa lineages undergo meiosis . Orthologs of genes employed in meiosis of sexual eukaryotes have recently been identified in
1638-404: The other groups, as illustrated below in a simplified diagram: Loukozoa [REDACTED] CRuMs [REDACTED] Amoebozoa Breviata [REDACTED] Apusomonadida [REDACTED] Fungi [REDACTED] Animalia [REDACTED] Strong similarities between Amoebozoa and Opisthokonts lead to the hypothesis that they form a distinct clade. Thomas Cavalier-Smith proposed
1680-617: 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
1722-440: The so-called "brain-eating amoeba" Naegleria fowleri , the intestinal parasite Entamoeba histolytica , which causes amoebic dysentery , and the multicellular "social amoeba" or slime mould Dictyostelium discoideum . Amoeba do not have cell walls, which allows for free movement. Amoeba move and feed by using pseudopods, which are bulges of cytoplasm formed by the coordinated action of actin microfilaments pushing out
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1764-427: The spelling to Amoeba . In 1841, Félix Dujardin coined the term " sarcode " (from Greek σάρξ sarx , "flesh," and εἶδος eidos , "form") for the "thick, glutinous, homogeneous substance" which fills protozoan cell bodies. Although the term originally referred to the protoplasm of any protozoan, it soon came to be used in a restricted sense to designate the gelatinous contents of amoeboid cells. Thirty years later,
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