Temporal range: Neoproterozoic–Recent
Lühe, 1913 emend. Cavalier-Smith, 1998
|Subphyla and Infraphyla|
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 most 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. Most phylogenetic trees identify it as the sister group to Opisthokonta, another major clade which contains both Fungi and Animals as well as some 300 species of unicellular protists. 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 symbiotes 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 varieties of slime molds, which have a macroscopic, multicellular stage of life during which individual amoeboid cells aggregate to produce spores.
Amoebozoa vary greatly in size. Some are only 10–20 μm in diameter, while others are among the largest protozoa. The well-known species Chaos and Pelomyxa (the so-called "giant amoebae") 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 1
- Place of Amoebozoa in the Eukaryote Tree 2.1
- Subphyla within Amoebozoat: Lobosa and Conosa 2.2
- Fossil record 3
- List of amoeboid protozoa pathogenic to humans 4
- References 5
- External links 6
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
- Molecular Phylogeny of Amoeboid Protists — Tree of Amoebozoa
- Tree of Life Eukaryotes
- Joseph Leidy's Amoeba Plates
- Schilde C, Schaap P (2013). "The Amoebozoa" (PDF). Methods Mol. Biol. Methods in Molecular Biology 983: 1–15.
- "Amoebozoa". NCBI Taxonomy Browser. 554915.
- Pawlowski; et al. (November 6, 2012). "CBOL Protist Working Group: Barcoding Eukaryotic Richness beyond the Animal, Plant, and Fungal Kingdoms". PLOS biology 10 (11).
- Adl; et al. (2012). "The Revised Classification of Eukaryotes". Journal of Eukaryotic Microbiology.
- Cavalier-Smith; et al. (2015). "Multigene phylogeny resolves deep branching of Amoebozoa". Molecular Phylogenetics and Evolution.
- Corliss, John O. (1984). "The Kingdom Protista and its 45 Phyla". BioSystems 17 (2): 87–126.
- Cavalier-Smith, Thomas (2003). "Protist phylogeny and the high-level classification of Protozoa". European Journal of Protistology.
- Derelle; et al. (2015). "Bacterial proteins pinpoint a single eukaryotic root". Proceedings of the National Academy of Sciences.
- "Zinc accumulation by the slime mold Fuligo septica (L.) Wiggers in the former Soviet Union and North Korea". Journal of Environment Quality 31 (3): 1038–42. 2002.
- Jeon, Kwang W. (1973). Biology of Amoeba. New York: Academic Press. p. 100.
- Eichinger, L.; Pachebat, J.A.; Glöckner, G.; Rajandream, M.A.; Sucgang, R.; Berriman, M.; Song, J.; Olsen, R.; Szafranski, K.; Xu, Q. (2005). "Dictyostelium discoideum"The genome of the social amoeba . Nature 435 (7038): 43–57.
- Cavalier-Smith, T.; Chao, E.E. (1996). "Molecular phylogeny of the free-living archezoan Trepomonas agilis and the nature of the first eukaryote". Journal of Molecular Evolution 43 (6): 551–562.
- Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews of the Cambridge Philosophical Society 73 (3): 203–266.
- Porter, Susannah H.; Meisterfeld, Ralf; Knoll, Andrew H. (2003). "Vase-shaped microfossils from the Neoproterozoic Chuar Group, Grand Canyon: a classification guided by modern testate amoebae". Journal of Paleontology 77 (3): 409–429.
- Porter, Susannah M. (2006). "The Proterozoic Fossil Record of Heterotrophic Eukaryotes". In Xiao, Shuhai; Kaufman, Alan J. Neoproterozoic Geolobiology and Paleobiology 27. Dordrecht, The Netherlands: Springer. pp. 1–21.
List of amoeboid protozoa pathogenic to humans
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.
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).
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.
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.
Subphyla within Amoebozoat: Lobosa and Conosa
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.
as illustrated below:
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,
Place of Amoebozoa in the Eukaryote Tree
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.
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.
While most amoebozoans are "naked," like the familiar Amoeba and Chaos, or covered with a loose coat of minute scales, like Arcella, or built up from collected particles cemented together, as in Difflugia.