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'{{Short description|Cellular body type}} {{About|the cellular body type|the genus|Amoeba (genus)|other uses|Amoeba (disambiguation)}} {{Use dmy dates|date=September 2020}}{{Use Oxford spelling|date=August 2016}} [[File:Amoeba collage.jpg|right|thumb|upright=1.5|Clockwise from top right: ''[[Amoeba proteus]]'', ''[[Actinophryid|Actinophrys sol]]'', ''[[Acanthamoeba]]'' sp., ''[[Nuclearia|Nuclearia thermophila]]''., ''[[Euglypha|Euglypha acanthophora]]'', [[neutrophil]] ingesting bacteria.]] An '''amoeba''' ({{IPAc-en|ə|ˈ|m|iː|b|ə}}; less commonly spelled '''ameba''' or '''amœba'''; {{plural form}}: '''amoebas''' (less commonly, '''amebas''') or '''amoebae''' ('''amebae''') {{IPAc-en|ə|ˈ|m|iː|b|i}}),<ref>[http://www.oxforddictionaries.com/definition/english/amoeba "Amoeba"] {{Webarchive|url=https://web.archive.org/web/20151122195608/http://www.oxforddictionaries.com/definition/english/amoeba |date=22 November 2015 }} at Oxforddictionaries.com</ref> often called an '''amoeboid''', is a type of [[Cell (biology)|cell]] or [[unicellular organism]] with the ability to alter its shape, primarily by extending and retracting [[pseudopodia|pseudopods]].<ref>{{Cite book|title=Dictionary of Microbiology and Molecular Biology, 3rd Edition, revised|url=https://archive.org/details/dictionarymicrob00sing_558|url-access=limited|last=Singleton|first=Paul|publisher=John Wiley & Sons|year=2006|isbn=978-0-470-03545-0 |location=Chichester, UK|pages=[https://archive.org/details/dictionarymicrob00sing_558/page/n42 32]}}</ref> Amoebae do not form a single [[Taxonomy (biology)|taxonomic group]]; instead, they are found in every major [[Lineage (evolution)|lineage]] of [[eukaryote|eukaryotic]] organisms. Amoeboid cells occur not only among the [[protozoa]], but also in [[fungi]], [[algae]], and [[animals]].<ref name=":1">{{cite web|url=http://tolweb.org/notes/?note_id=51|title=Amoebae: Protists Which Move and Feed Using Pseudopodia|author=David J. Patterson|publisher=Tree of Life web project|access-date=21 September 2009|archive-url=https://web.archive.org/web/20100615015212/http://tolweb.org/notes/?note_id=51|archive-date=15 June 2010|url-status=live}}</ref><ref>{{cite web|url=http://www.bms.ed.ac.uk/research/others/smaciver/amoebae.htm |title=The Amoebae |publisher=The University of Edinburgh |url-status=dead |archive-url=https://web.archive.org/web/20090610035748/http://www.bms.ed.ac.uk/research/others/smaciver/amoebae.htm |archive-date=10 June 2009 }}</ref><ref>{{cite web|url=http://www.microscopy-uk.org.uk/mag/wimsmall/sundr.html|title=Sun animalcules and amoebas|author=Wim van Egmond|publisher=Microscopy-UK|access-date=23 October 2005|archive-url=https://web.archive.org/web/20051104122947/http://microscopy-uk.org.uk/mag/wimsmall/sundr.html|archive-date=4 November 2005|url-status=live}}</ref><ref>{{Cite journal|last1=Flor-Parra |first1=Ignacio |last2=Bernal |first2=Manuel |last3=Zhurinsky |first3=Jacob |last4=Daga |first4=Rafael R.|date=2013-12-17|title=Cell migration and division in amoeboid-like fission yeast |journal=Biology Open |volume=3 |issue=1 |pages=108–115|doi=10.1242/bio.20136783 |issn=2046-6390|pmc=3892166 |pmid=24357230}}</ref><ref>{{Cite journal |last1=Friedl |first1=P. |last2=Borgmann|first2=S.|last3=Bröcker|first3=E. B.|date=2001-10-01|title=Amoeboid leukocyte crawling through extracellular matrix: lessons from the Dictyostelium paradigm of cell movement|journal=Journal of Leukocyte Biology |volume=70|issue=4 |pages=491–509 |doi=10.1189/jlb.70.4.491 |issn=0741-5400|pmid=11590185|s2cid=28731650 }}</ref> [[Microbiologist]]s often use the terms "amoeboid" and "amoeba" interchangeably for any organism that exhibits [[amoeboid movement]].<ref name=":0">{{cite journal |last1=Marée |first1=Athanasius FM |last2=Hogeweg |first2=Paulien |year=2001 |title=How amoeboids self-organize into a fruiting body: multicellular coordination in Dictyostelium discoideum |journal=Proceedings of the National Academy of Sciences |volume=98 |issue=7|pages=3879–3883 |doi=10.1073/pnas.061535198 |pmid=11274408 |pmc=31146 |doi-access=free }}</ref><ref>{{cite journal |last1=Mackerras |first1=M. J. |last2=Ercole |first2=Q. N. |year=1947 |title=Observations on the action of paludrine on malarial parasites |journal=Transactions of the Royal Society of Tropical Medicine and Hygiene |volume=41 |issue=3|pages=365–376 |doi=10.1016/s0035-9203(47)90133-8 |pmid=18898714 }}</ref> In older classification systems, most amoebae were placed in the [[Class (biology)|class]] or [[subphylum]] Sarcodina, a grouping of [[Unicellular organism|single-celled organisms]] that possess pseudopods or move by [[protoplasm]]ic 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.<ref name="Pawlowski">Jan Pawlowski: ''The twilight of Sarcodina: a molecular perspective on the polyphyletic origin of amoeboid protists''. Protistology, Band 5, 2008, S. 281–302. [http://protistology.ifmo.ru/num5_4/pawlowski.pdf (pdf, 570 kB)] {{Webarchive|url=https://web.archive.org/web/20130614123442/http://protistology.ifmo.ru/num5_4/pawlowski.pdf |date=14 June 2013 }}</ref> The best known amoeboid [[protists]] are ''[[Chaos carolinense]]'' and ''[[Amoeba proteus]]'', both of which have been widely cultivated and studied in classrooms and laboratories.<ref>{{Cite journal|last=Tan|display-authors=et al|date=2005|title=A simple mass culture of the amoeba Chaos carolinense: revisit|url=http://protistology.ifmo.ru/num4_2/tan.pdf|journal=Protistology|volume=4|pages=185–90|access-date=28 September 2017|archive-url=https://web.archive.org/web/20170929000449/http://protistology.ifmo.ru/num4_2/tan.pdf|archive-date=29 September 2017|url-status=live}}</ref><ref>{{Cite news|url=https://davidwangblog.wordpress.com/relationship-with-humans/|title=Relationship with Humans|date=2013-04-12|work=Amoeba proteus|access-date=2017-09-28|language=en-US|archive-url=https://web.archive.org/web/20170929000804/https://davidwangblog.wordpress.com/relationship-with-humans/|archive-date=29 September 2017|url-status=live}}</ref> Other well known species include 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]]''. '''''Italic text''''''''Italic text'''''''''Bold text'''''''''Bold text'''''''''Bold text'''''''''Bold text'''''''''Bold text'''''''''Bold text'''''''''Bold text''''''Bold text''''''''''''''''''''''''''''==Shape, movement and nutrition== [[File:PseudopodiaFormsDavidPatterson.jpg|thumb|380px|right|The forms of [[pseudopodia]], from left: polypodial and lobose; monopodial and lobose; filose; conical; reticulose; tapering actinopods; non-tapering actinopods]] 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 the [[plasma membrane]] that surrounds the cell.<ref>{{Cite book|title=Molecular Biology of the Cell 5th Edition|last=Alberts Eds.|publisher=Garland Science|year=2007|isbn=9780815341055|location=New York|pages=1037|display-authors=etal}}</ref> 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 (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 the [[Radiolaria]] and [[Heliozoa]], have stiff, needle-like, radiating [[pseudopodia#Morphology|axopodia]] (actinopoda) supported from within by bundles of [[microtubules]].<ref name=":1"/><ref>{{Cite book|title=Kingdoms and Domains|url=https://archive.org/details/fivekingdomsillu00marg_711|url-access=limited|last=Margulis|first=Lynn|author-link=Lynn Margulis|publisher=Academic Press|year=2009|isbn=978-0-12-373621-5|pages=[https://archive.org/details/fivekingdomsillu00marg_711/page/n261 206]–7}}</ref> {{Multiple image |total_width=380 |image1=Строение амебы Mayorella sp.jpg |alt1=Naked amoeba in the genus Mayorella |image2=Difflugia acuminata.jpg |alt2=Shell of the testate amoeba Cylindrifflugia acuminata |footer="Naked" amoeba of the genus ''[[Mayorella]]'' (left) and shell of the [[testate amoeba]] ''Cylindrifflugia acuminata'' (right) }} Free-living amoebae may be "[[testate amoebae|testate]]" (enclosed within a hard shell), or "naked" (also known as [[wikispecies:gymnamoebae|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 the [[frustules]] of [[diatoms]].<ref>{{Cite book|title=An Atlas of Freshwater Testate Amoeba|last=Ogden|first=C. G.|publisher=Oxford University Press, for British Museum (Natural History)|year=1980|isbn=978-0198585022|location=Oxford, London, and Glasgow|pages=1–5}}</ref> To regulate [[osmotic pressure]], most freshwater amoebae have a contractile [[vacuole]] which expels excess water from the cell.<ref>{{Cite book|title=Molecular Biology of the Cell 5th Edition|last=Alberts Eds.|publisher=Garland Science|year=2007|isbn=9780815341055|location=New York|pages=663|display-authors=etal}}</ref> 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 [[tonicity|hypotonic]] with respect to the contents of the cell, water 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.<ref>Kudo, Richard Roksabro. "Protozoology." Protozoology 4th Edit (1954). p. 83</ref> ==Diet== [[File:Phagocytosis -- amoeba.jpg|thumb|300px|Amoeba [[phagocytosis]] of a [[bacterium]]]] The food sources of amoebae vary. Some amoebae are predatory and live by consuming bacteria and other [[protist]]s. Some are [[detritivore]]s 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 a mouth or [[cytostome]], and there is no fixed place on the cell at which phagocytosis normally occurs.<ref>Thorp, James H. (2001). Ecology and Classification of North American Freshwater Invertebrates. San Diego: Academic. p. 71. {{ISBN|0-12-690647-5}}.</ref> Some amoebae also feed by [[pinocytosis]], imbibing dissolved nutrients through [[Vesicle (biology and chemistry)|vesicles]] formed within the cell membrane.<ref>{{Cite book|title=Biology of Amoeba|url=https://archive.org/details/biologyofamoeba0000jeon|url-access=registration|last=Jeon|first=Kwang W.|publisher=Academic Press|year=1973|location=New York|pages=[https://archive.org/details/biologyofamoeba0000jeon/page/100 100]|isbn=9780123848505}}</ref> ==Size range== [[File: Ammonia tepida.jpg|thumb|[[Foraminifera]] have reticulose (net-like) pseudopods, and many species are visible with the naked eye]] The size of amoeboid cells and species is extremely variable. The marine amoeboid ''[[Massisteria|Massisteria voersi]]'' is just 2.3 to 3 [[micrometre]]s in diameter,<ref name="Mylnikov">{{Cite journal|last1=Mylnikov|first1=Alexander P.|last2=Weber|first2=Felix|last3=Jürgens|first3=Klaus|last4=Wylezich|first4=Claudia|date=2015-08-01|title=Massisteria marina has a sister: Massisteria voersi sp. nov., a rare species isolated from coastal waters of the Baltic Sea|journal=European Journal of Protistology|volume=51|issue=4|pages=299–310|doi=10.1016/j.ejop.2015.05.002|issn=1618-0429|pmid=26163290}}</ref> within the size range of many bacteria.<ref>{{Cite web|url=http://classes.midlandstech.edu/carterp/courses/bio225/chap04/lecture2.htm|title=The Size, Shape, And Arrangement of Bacterial Cells|website=classes.midlandstech.edu|access-date=2016-08-21|archive-url=https://web.archive.org/web/20160809135552/http://classes.midlandstech.edu/carterp/courses/bio225/chap04/lecture2.htm|archive-date=9 August 2016|url-status=dead}}</ref> At the other extreme, the shells of deep-sea [[xenophyophore]]s can attain 20&nbsp;cm in diameter.{{r|gooday2011}} Most of the free-living freshwater amoebae commonly found in [[pond life|pond water]], ditches, and lakes are [[Microscopic scale|microscopic]], but some species, such as the so-called "giant amoebae" [[Pelomyxa|''Pelomyxa palustris'']] and [[Chaos (genus)|''Chaos carolinense'']], can be large enough to see with the naked eye. {|class="wikitable" |- ! Species or cell type ! Size in micrometers |- |''[[Massisteria|Massisteria voersi]]''<ref name=Mylnikov/> |2.3–3 |- |''[[Naegleria fowleri]]''<ref>{{Cite web|url=http://www.webmd.com/brain/brain-eating-amoeba#1|title=Brain-Eating Amoeba (Naegleria Fowleri): Causes and Symptoms|language=en-US|access-date=2016-08-21|archive-url=https://web.archive.org/web/20160821233242/http://www.webmd.com/brain/brain-eating-amoeba#1|archive-date=21 August 2016|url-status=live}}</ref> |8–15 |- |[[Neutrophil]] (white blood cell)<ref>{{Cite web|url=http://www.anatomyatlases.org/MicroscopicAnatomy/Section04/Section04.shtml|title=Anatomy Atlases: Atlas of Microscopic Anatomy: Section 4: Blood|website=www.anatomyatlases.org|access-date=2016-08-21|archive-url=https://web.archive.org/web/20160819003652/http://www.anatomyatlases.org/MicroscopicAnatomy/Section04/Section04.shtml|archive-date=19 August 2016|url-status=live}}</ref> |12–15 |- |''[[Acanthamoeba]]''<ref>{{Cite web|url=http://www.arcella.nl/acanthamoeba|title=''Acanthamoeba'' {{!}} Microworld|website=www.arcella.nl|access-date=2016-08-21|archive-url=https://web.archive.org/web/20160818072935/http://arcella.nl/acanthamoeba|archive-date=18 August 2016|url-status=dead}}</ref> |12–40 |- |''[[Entamoeba histolytica]]''<ref>{{Cite web|url=https://msu.edu/course/zol/316/ehisscope.htm|title=Microscopy of ''Entamoeba histolytica''|website=msu.edu|access-date=2016-08-21|archive-url=https://web.archive.org/web/20161005024303/https://msu.edu/course/zol/316/ehisscope.htm|archive-date=5 October 2016|url-status=live}}</ref> |15–60 |- |''[[Arcella|Arcella vulgaris]]''<ref>{{Cite web|url=http://www.arcella.nl/arcella-vulgaris|title=''Arcella vulgaris'' {{!}} Microworld|website=www.arcella.nl|access-date=2016-08-21|archive-url=https://web.archive.org/web/20160818211646/http://arcella.nl/arcella-vulgaris|archive-date=18 August 2016|url-status=live}}</ref> |30–152 |- |''[[Amoeba proteus]]''<ref>{{Cite web|url=http://www.arcella.nl/amoeba-proteus|title=''Amoeba proteus'' {{!}} Microworld|website=www.arcella.nl|access-date=2016-08-21|archive-url=https://web.archive.org/web/20160818214156/http://arcella.nl/amoeba-proteus|archive-date=18 August 2016|url-status=live}}</ref> |220–760 |- |''[[Chaos carolinense]]''<ref>{{Cite web|url=http://www.arcella.nl/chaos|title=''Chaos'' {{!}} Microworld|website=www.arcella.nl|access-date=2016-08-21|archive-url=https://web.archive.org/web/20161012224818/http://arcella.nl/chaos|archive-date=12 October 2016|url-status=live}}</ref> |700–2000 |- |''[[Pelomyxa|Pelomyxa palustris]]''<ref>{{Cite web|url=http://www.arcella.nl/pelomyxa-palustris|title=''Pelomyxa palustris'' {{!}} Microworld|website=www.arcella.nl|access-date=2016-08-21|archive-url=https://web.archive.org/web/20160818072933/http://arcella.nl/pelomyxa-palustris|archive-date=18 August 2016|url-status=live}}</ref> |up to 5000 |- |''[[Syringammina fragilissima]]''{{r|gooday2011}} |up to {{val|200000}} |- |} ==Amoebae as specialized cells and life cycle stages== [[File:Neutrophil with anthrax copy.jpg|thumb|[[Neutrophil]] (white blood cell) engulfing anthrax bacteria]] Some [[multicellular organisms]] have amoeboid cells only in certain phases of life, or use amoeboid movements for specialized functions. In the immune system of humans and other animals, amoeboid [[white blood cells]] pursue invading organisms, such as bacteria and pathogenic protists, and engulf them by [[phagocytosis]].<ref>{{cite journal |last1=Friedl |first1=Peter |last2=Borgmann |first2=Stefan |last3=Eva-B |first3=Bröcker |year=2001 |title=Amoeboid leukocyte crawling through extracellular matrix: lessons from the Dictyostelium paradigm of cell movement |journal=Journal of Leukocyte Biology |volume=70 |issue=4|pages=491–509 |doi=10.1189/jlb.70.4.491 |pmid=11590185 |s2cid=28731650 }}</ref> Amoeboid stages also occur in the multicellular fungus-like protists, the so-called [[slime mold|slime mould]]s. Both the plasmodial slime moulds, currently classified in the class [[Myxogastria]], and the cellular slime moulds of the groups [[Acrasida]] and [[Dictyosteliida]], live as amoebae during their feeding stage. The amoeboid cells of the former combine to form a giant [[multinucleate]] organism,<ref>{{Cite journal|title=Intelligence: Maze-solving by an amoeboid organism|last=Nakagaki|date=2000|journal=Nature|doi=10.1038/35035159|pmid=11028990|volume=407|issue=6803|pages=470|display-authors=etal|bibcode=2000Natur.407..470N|s2cid=205009141|doi-access=free}}</ref> while the cells of the latter live separately until food runs out, at which time the amoebae aggregate to form a multicellular migrating "slug" which functions as a single organism.<ref name=":0" /> Other organisms may also present amoeboid cells during certain life-cycle stages, e.g., the gametes of some green algae ([[Zygnematophyceae]])<ref>{{Cite book|title=Freshwater Algae of North America|url=https://archive.org/details/freshwateralgaen00shea|url-access=limited|last=Wehr|first=John D.|publisher=Academic Press|year=2003|isbn=978-0-12-741550-5|location=San Diego and London|pages=[https://archive.org/details/freshwateralgaen00shea/page/n369 353]}}</ref> and pennate [[diatoms]],<ref>{{Cite web|url=http://rbg-web2.rbge.org.uk/algae/auxospores/lifecycle_sexual.html|title=Algae World: diatom sex and life cycles|access-date=1 March 2015|website=Algae World|publisher=Royal Botanic Garden Edinburgh|archive-url=https://web.archive.org/web/20140923102400/http://rbg-web2.rbge.org.uk/algae/auxospores/lifecycle_sexual.html|archive-date=23 September 2014|url-status=live}}</ref> the spores (or dispersal phases) of some [[Mesomycetozoea]],<ref>{{Cite journal|title=New species of Paramoebidium (trichomycetes, Mesomycetozoea) from the Mediterranean, with comments about the amoeboid cells in Amoebidiales|last=Valle|first=L.G.|date=2014|journal=Mycologia|doi=10.3852/13-153|pmid=24895422|volume=106|issue=3|pages=481–90|s2cid=3383757}}</ref><ref>Taylor, J. W. & Berbee, M. L. (2014). Fungi from PCR to Genomics: The Spreading Revolution in Evolutionary Biology. In: ''Systematics and Evolution''. Springer Berlin Heidelberg. p. 52, [https://books.google.com/books?id=SuZhBAAAQBAJ&pg=PA10] {{Webarchive|url=https://web.archive.org/web/20150630063053/https://books.google.com/books?id=SuZhBAAAQBAJ&lpg=PP1&hl=&pg=PA10|date=30 June 2015}}</ref> and the [[sporoplasm]] stage of [[Myxozoa]] and of [[Ascetosporea]].<ref>{{cite journal |last1=Corliss |first1=J. O. |year=1987 |title=Protistan phylogeny and eukaryogenesis |url=https://books.google.com/books?id=oIbZPrCEvYwC |journal=International Review of Cytology |volume=100 |pages=319–370 |doi=10.1016/S0074-7696(08)61703-9 |pmid=3549607 |isbn=9780080586373 }}</ref> {{Clear}} ==Amoebae as taxa== ===Early history and origins of Sarcodina=== [[File:Der Kleine Proteus from Roesel.jpg|thumb|250x250px|The first illustration of an amoeboid, from Roesel von Rosenhof's ''Insecten-Belustigung'' (1755)]] [[File:Amoeba proteus with many pseudopodia.jpg|thumb|''Amoeba proteus''|250x250px]] 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").<ref>Rosenhof, R. (1755). ''Monatlich herausgegebene Insektenbelustigungen'', vol. 3, p. 621, [https://books.google.com/books?id=q9JCAQAAMAAJ&pg=PA621] {{Webarchive|url=https://web.archive.org/web/20150713174920/https://books.google.com/books?id=q9JCAQAAMAAJ&hl=&pg=PA621|date=13 July 2015}}.</ref> Rösel's illustrations show an unidentifiable freshwater amoeba, similar in appearance to the common species now known as [[Amoeba proteus]].<ref>{{Cite book|title=Biology of Amoeba|url=https://archive.org/details/biologyofamoeba0000jeon|url-access=registration|last=Jeon|first=Kwang W.|publisher=Academic Press |date=1973 |location=New York|pages=2–3, [https://books.google.com/books?id=J0vniMFGPukC&pg=PA2]|isbn=9780123848505}}</ref> The term "Proteus animalcule" remained in use throughout the 18th and 19th centuries, as an informal name for any large, free-living amoeboid.<ref>{{Cite book|title=Biological atlas: a guide to the practical study of plants and animals|url=https://archive.org/details/biologicalatlasg00mcal|last=McAlpine|first=Daniel|publisher=W. & A. K. Johnston |date=1881 |location=Edinburgh and London|pages=[https://archive.org/details/biologicalatlasg00mcal/page/17 17]}}</ref> In 1822, the genus ''Amiba'' (from the [[Ancient Greek|Greek]] ἀμοιβή ''amoibe'', meaning "change") was erected by the French naturalist [[Bory de Saint-Vincent]].<ref>Bory de Saint-Vincent, J. B. G. M. "Essai d'une classification des animaux microscopiques." Agasse, Paris (1826).p. 28</ref><ref name="EOS1">{{cite book |editor1-first=Kimberley |editor1-last=McGrath |editor2-last=Blachford |editor2-first=Stacey |title=Gale Encyclopedia of Science Vol. 1: Aardvark-Catalyst |edition=2nd |date=2001 |isbn=978-0-7876-4370-6 |publisher=Gale Group |oclc=46337140 |url-access=registration |url=https://archive.org/details/galeencyclopedia0000mcgr }}</ref> Bory's contemporary, [[C. G. Ehrenberg]], adopted the genus in his own classification of microscopic creatures, but changed the spelling to ''Amoeba''.<ref>Ehrenberg, Christian Gottfried. Organisation, systematik und geographisches verhältniss der infusionsthierchen: Zwei vorträge, in der Akademie der wissenschaften zu Berlin gehalten in den jahren 1828 und 1830. Druckerei der Königlichen akademie der wissenschaften, 1832. p. 59</ref> 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.<ref>{{Cite book|title=Histoire Naturelle des Zoophytes Infusoires|url=https://archive.org/details/histoirenaturelle00duja|last=Dujardin|first=Felix|publisher=Librarie Encyclopedique de Roret |date=1841 |location=Paris|pages=[https://archive.org/details/histoirenaturelle00duja/page/26 26]}}</ref> 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.<ref name="Pawlowski"/> Thirty years later, 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".<ref>{{Cite book|title=Zoologie|url=https://archive.org/details/zoologie00schmgoog|last=Schmarda|first=Ludwig Karl|publisher=W. Braumüller |date=1871 |pages=[https://archive.org/details/zoologie00schmgoog/page/n173 156]}}</ref> Later workers, including the influential taxonomist [[Otto Bütschli]], amended this group to create the class Sarcodina,<ref>{{Cite book|title=Klassen und Ordnungen des Thier-Reichs I. Abteilung: Sarkodina und Sporozoa|last=Bütschli|first=Otto|publisher=Paleontologische Entwicklung der Rhisopoda von C. Scwager |date=1882 |pages=1}}</ref> a [[taxon]] that remained in wide use throughout most of the 20th century. Within the traditional Sarcodina, amoebae were generally divided into [[Morphology (biology)|morphological categories]], on the basis of the form and structure of their [[pseudopod]]s. Amoebae with pseudopods supported by regular arrays of [[microtubule]]s (such as the freshwater [[Heliozoa]] and marine [[Radiolaria]]) were classified as [[species:Actinopoda#Calkins .281909.29|Actinopoda]]; whereas those with unsupported pseudopods were classified as [[species:Rhizopoda|Rhizopoda]].<ref>{{Cite book|title=Protozoölogy|url=https://archive.org/details/in.ernet.dli.2015.166964|last=Calkins|first=Gary N.|publisher=Lea & Febiger |date=1909 |location=New York|pages=[https://archive.org/details/in.ernet.dli.2015.166964/page/n106 38]–40}}</ref> The Rhizopods were further subdivided into lobose, filose, and reticulose amoebae, according to the morphology of their pseudopods. ===Dismantling of Sarcodina=== In the final decade of the 20th century, a series of molecular phylogenetic analyses confirmed that Sarcodina was not a [[monophyletic]] group. In view of these findings, the old scheme was abandoned and the amoebae of Sarcodina were dispersed among many other high-level taxonomic groups. Today, the majority of traditional sarcodines are placed in two eukaryote [[Kingdom (biology)#Eukaryotic supergroups|supergroups]]: [[Amoebozoa]] and [[Rhizaria]]. The rest have been distributed among the [[Excavata|excavates]], [[opisthokonts]], and [[stramenopiles]]. Some, like the [[Centrohelida]], have yet to be placed in any supergroup.<ref name="Pawlowski"/><ref>{{Cite journal|title=The Revised Classification of Eukaryotes|last=Adl|first=Sina M.|date=2012|journal=Journal of Eukaryotic Microbiology|doi=10.1111/j.1550-7408.2012.00644.x|pmid=23020233|display-authors=etal|volume=59|issue=5|pages=429–93|pmc=3483872}}</ref> ===Classification=== Recent classification places the various amoeboid genera in the following groups: {|class="wikitable" |- ! Supergroups ! Major groups and genera ! Morphology |- |[[Amoebozoa]] | * '''[[Tubulinea]]''' (formerly part of [[Lobosa]]) ** [[Amoeba (genus)|Amoeba]], [[Chaos (amoeba)|Chaos]], [[Hydramoeba]], [[Metachaos]], [[Trichamoeba]], [[Glaeseria]], [[Hartmannella]],[[Polychaos]], [[Saccamoeba]], [[Flabellula]], [[Gephyramoeba]], [[Leptomyxa]], [[Rhizamoeba]], [[Trichosphaerium]], [[Echinamoeba]], * '''[[Discosea]]''' (formerly part of Lobosa) ** ''[[Acanthamoeba]], [[Protoacanthamoeba]], [[Balamuthia]], [[Discamoeba]], [[Clydonella]], [[Hollandella]], [[Korotnevella]] (Dactylamoeba), [[Lingulamoeba]], [[Mayorella]], [[Neoparamoeba]], [[Paramoeba]], [[Platyamoeba]], [[Sappinia]], [[Thecamoeba]], [[Unda (genus)|Unda]], [[Vannella]], [[Vexillifera]]'' *[[Conosa]]: ** ''[[Endamoeba]]'', ''[[Entamoeba]]'', [[Filamoeba]], ''[[Iodamoeba]]'', ''[[Mastigamoeba]]'', [[Mastigina]], [[Phreatamoeba]],''[[Mastigella]]'', ''[[Pelomyxa]]'', ''[[Dictyostelium]]'', ''[[Physarum]]'' * ''incertae sedis'' ** Stereomyxa |valign=top| * Lobose pseudopods ([[Lobosa]]) are blunt, and there may be one or several on a cell, which is usually divided into a layer of clear ectoplasm surrounding more granular endoplasm. |- |[[Rhizaria]] |valign=top| * [[Cercozoa]]: **'''[[Filosa]]''': ***'''[[Monadofilosa]]''': ''[[Gyromitus]]'', ''[[Paulinella]]'' ***'''[[Granofilosea]]''' ***[[Chlorarachniophyceae]] **'''[[Endomyxa]]''': ***[[Proteomyxidea]]: orders [[Aconchulinida]], [[Pseudosporida]], [[Reticulosida]] ***[[Gromiidea]] * [[Foraminifera]] * [[Radiolaria]] |valign=top| * Filose pseudopods ([[Filosa]]) are narrow and tapering. The vast majority of filose amoebae, including all those that produce shells, are placed within the [[Cercozoa]] together with various flagellates that tend to have amoeboid forms. The naked filose amoebae also includes [[vampyrellid]]s. * Reticulose pseudopods ([[Endomyxa]]) are cytoplasmic strands that branch and merge to form a net. They are found most notably among the [[Foraminifera]], a large group of marine protists that generally produce multi-chambered shells. There are only a few sorts of naked reticulose amoebae, notably the [[gymnophryid]]s, and their relationships are not certain. * [[Radiolaria]]ns are a subgroup of actinopods that are now grouped with rhizarians. |- |[[Excavata]] |valign=top| * '''[[Heterolobosea]]''': **[[Vahlkampfiidae]]: ''[[Monopylocystis]]'', ''[[Naegleria]]'', ''[[Neovahlkampfia]]'', ''[[Paratetramitus]]'', ''[[Paravahlkampfia]]'', ''[[Protonaegleria]]'', ''[[Psalteriomonas]]'', ''[[Sawyeria]]'', ''[[Tetramitus]]'', ''[[Vahlkampfia]]'', ''[[Willaertia]]'' **[[Gruberellidae]]: ''[[Gruberella]]'', ''[[Stachyamoeba]]'' *[[Parabasalidea]]: ''[[Dientamoeba]]'', ''[[Histomonas]]'' *Other: ''[[Rosculus]]'', ''[[Acrasis]]'', ''[[Heteramoeba]]'', ''[[Learamoeba]]'', ''[[Stygamoeba]]'', ''[[Plaesiobystra]]'',<ref name="Park2009">{{Cite journal |last1=Park |first1=J. S. |last2=Simpson |first2=A. G. B. |last3=Brown |first3=S. |last4=Cho |first4=B. C. |title=Ultrastructure and Molecular Phylogeny of two Heterolobosean Amoebae, Euplaesiobystra hypersalinica gen. Et sp. Nov. And Tulamoeba peronaphora gen. Et sp. Nov., Isolated from an Extremely Hypersaline Habitat |doi=10.1016/j.protis.2008.10.002 |journal=Protist |volume=160 |issue=2 |pages=265–283 |date=2009 |pmid=19121603}}</ref> ''[[Tulamoeba]]''<ref name="Park2009" /> |valign=top| * The [[Heterolobosea]], includes protists that can transform between amoeboid and [[flagellate]] forms. |- |[[Heterokonta]] |valign=top| * [[Chrysophyceae]]: ''Chrysamoeba'', ''Rhizochrysis'' * [[Xanthophyceae]]: ''Rhizochloris'' * [[Labyrinthulomycetes]] | * The heterokont chrysophyte and xanthophyte algae include some amoeboid members, the latter being poorly studied.<ref>Ott, Donald W., Carla K. Oldham-Ott, Nataliya Rybalka, and Thomas Friedl. 2015. Xanthophyte, Eustigmatophyte, and Raphidophyte Algae. In: Wehr, J.D., Sheath, R.G., Kociolek, J.P. (Eds.) ''Freshwater Algae of North America: Ecology and Classification'', 2nd edition. Academic Press, Amsterdam, pp. 483–534, [https://books.google.com/books?id=yjnLAwAAQBAJ] {{Webarchive|url=https://web.archive.org/web/20170122104643/https://books.google.com/books?id=yjnLAwAAQBAJ|date=22 January 2017}}.</ref> |- |[[Alveolata]] |valign=top| * [[Dinoflagellate|Dinoflagellata]]: ''[[Oodinium]]'', ''[[Pfiesteria]]'' | * Parasite with amoeboid life cycle stages. |- |[[Opisthokont]]a |valign=top| * Nucleariida: ''[[Micronuclearia]]'', ''[[Nuclearia]]'' |valign=top| * [[Nucleariid]]s appear to be close relatives of animals and [[Fungus|fungi]]. |- |{{vanchor|Ungrouped}}/<br />unknown |valign=top| * ''Adelphamoeba'', ''Astramoeba'', ''Dinamoeba'', ''Flagellipodium'', ''Flamella'', ''Gibbodiscus'', ''Gocevia'', ''Malamoeba'', ''Nollandia'', ''Oscillosignum'', ''Paragocevia'', ''[[Parvamoeba]]'', ''Pernina'', ''Pontifex'', ''Pseudomastigamoeba'', ''Rugipes'', ''Striamoeba'', ''Striolatus'', ''Subulamoeba'', ''Theratromyxa'', ''Trienamoeba'', ''Trimastigamoeba'', and over 40 other genera<ref>Patterson, D. J.; Simpson, A. G. B.; Rogerson, A. (2000). "Amoebae of uncertain affinities". In: Lee, J. J.; Leedale, G. F.; Bradbury, P. ''An Illustrated Guide to the Protozoa'', 2nd ed., Vol. 2, p. 804-827. Lawrence, Kansas: Society of Protozoologists/Allen Press. [https://species.wikimedia.org/wiki/Incertae_sedis_Eukaryota#Patterson.2C_Simpson.2C_.26_Rogerson.2C_in_Lee_et_al._.282000.29] {{Webarchive|url=https://web.archive.org/web/20160308194141/https://species.wikimedia.org/wiki/Incertae_sedis_Eukaryota#Patterson.2C_Simpson.2C_.26_Rogerson.2C_in_Lee_et_al._.282000.29 |date=8 March 2016}}. Genera considered ungrouped/unknown by this source in 2000 but which have since become classified have been moved to those classifications on Wikipedia.</ref> | |} Some of the amoeboid groups cited (e.g., part of [[chrysophyte]]s, part of [[xanthophyte]]s, [[chlorarachniophyte]]s) were not traditionally included in Sarcodina, being classified as [[algae]] or [[flagellate]]d protozoa. ==Pathogenic interactions with other organisms== [[File:Trophozoites of Entamoeba histolytica with ingested erythrocytes.JPG|thumb|[[Trophozoite]]s of the pathogenic ''[[Entamoeba histolytica]]'' with ingested [[red blood cell]]s]] Some amoebae can infect other organisms [[pathogen]]ically, causing disease:<ref>Casadevall A (2008) Evolution of intracellular pathogens. Annu Rev Microbiol 62: 19–33. 10.1146/annurev.micro.61.080706.093305 [PubMed] [CrossRef] [Google Scholar]</ref><ref>Guimaraes AJ, Gomes KX, Cortines JR, Peralta JM, Peralta RHS (2016) Acanthamoeba spp. as a universal host for pathogenic microorganisms: One bridge from environment to host virulence. Microbiological Research 193: 30–38. 10.1016/j.micres.2016.08.001 [PubMed] [CrossRef] [Google Scholar]</ref><ref>Hilbi H, Weber SS, Ragaz C, Nyfeler Y, Urwyler S (2007) Environmental predators as models for bacterial pathogenesis. Environmental microbiology 9: 563–575. 10.1111/j.1462-2920.2007.01238.x [PubMed] [CrossRef] [Google Scholar]</ref><ref>{{cite journal |last1=Greub |first1=G |last2=Raoult |first2=D |year=2004 |title=Microorganisms resistant to free-living amoebae |journal=Clinical Microbiology Reviews |volume=17 |issue=2 |pages=413–433 |doi=10.1128/CMR.17.2.413-433.2004 |pmid=15084508 |pmc=387402 |doi-access=free }}</ref> *''[[Entamoeba histolytica]]'' is the cause of [[amoebiasis]], or amoebic dysentery. *''[[Naegleria fowleri]]'' (the "brain-eating amoeba") is a fresh-water-native species that can be fatal to humans if introduced through the nose. *''[[Acanthamoeba]]'' can cause amoebic [[keratitis]] and [[encephalitis]] in humans. *''[[Balamuthia mandrillaris]]'' is the cause of (often fatal) [[granulomatous amoebic meningoencephalitis]]. Amoeba have been found to harvest and grow the bacteria implicated in [[Plague (disease)|plague]].<ref>{{Cite web|url=https://www.sciencedaily.com/releases/2018/01/180116144229.htm|title = Are amoebae safe harbors for plague? New research shows that plague bacteria not only survive, but thrive and replicate once ingested by an amoeba}}</ref> 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.{{r|vid2016}} The currently generally utilized and best-explored amoebae that host other organisms are Acanthamoeba castellanii and Dictyostelium discoideum.<ref>{{Cite journal |doi=10.3389/fcimb.2019.00047|pmid=30941316|title=Editorial: Amoebae as Host Models to Study the Interaction with Pathogens |year=2019|last1=Thewes|first1=Sascha|last2=Soldati|first2=Thierry|last3=Eichinger |first3=Ludwig|journal=Frontiers in Cellular and Infection Microbiology|volume=9|doi-access=free|pmc=6433779|page=47}}</ref> Microorganisms that can overcome the defenses of one-celled organisms can shelter and multiply inside them, where they are shielded from unfriendly outside conditions by their hosts. ==Meiosis== Recent evidence indicates that several Amoebozoa lineages undergo [[meiosis]]. [[Homology (biology)#Orthology|Orthologs]] of genes employed in [[meiosis]] of sexual [[eukaryote]]s have recently been identified in the ''[[Acanthamoeba]]'' [[genome]]. These genes included ''[[Spo11]], [[MRE11A|Mre11]], [[Rad50]], [[RAD51|Rad51]], [[RAD52|Rad52]], Mnd1, [[DMC1 (gene)|Dmc1]], [[MSH2|Msh]]'' and ''[[MLH1#Meiosis|Mlh]]''.<ref name="pmid25800982">{{cite journal |vauthors=Khan NA, Siddiqui R |title=Is there evidence of sexual reproduction (meiosis) in Acanthamoeba? |journal=Pathog Glob Health |volume=109 |issue=4 |pages=193–5 |year=2015 |pmid=25800982 |doi=10.1179/2047773215Y.0000000009 |pmc=4530557 }}</ref> 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 (gene)|Dmc1]], is required for efficient meiotic [[homologous recombination]], and ''Dmc1'' is expressed in ''[[Entamoeba histolytica]]''.<ref name=Kelso>{{cite journal |vauthors=Kelso AA, Say AF, Sharma D, Ledford LL, Turchick A, Saski CA, King AV, Attaway CC, Temesvari LA, Sehorn MG |title=Entamoeba histolytica Dmc1 Catalyzes Homologous DNA Pairing and Strand Exchange That Is Stimulated by Calcium and Hop2-Mnd1 |journal=PLOS ONE |volume=10 |issue=9 |pages=e0139399 |year=2015 |pmid=26422142 |pmc=4589404 |doi=10.1371/journal.pone.0139399 |bibcode=2015PLoSO..1039399K |doi-access=free }}</ref> The purified Dmc1 from ''E. histolytica'' forms [[Synapsis|presynaptic]] filaments and catalyses [[Adenosine triphosphate|ATP]]-dependent [[Homologous recombination|homologous DNA pairing]] and DNA strand exchange over at least several thousand [[base pairs]].<ref name=Kelso /> The DNA pairing and strand exchange reactions are enhanced by the eukaryotic meiosis-specific recombination accessory factor (heterodimer) Hop2-Mnd1.<ref name=Kelso /> These processes are central to meiotic recombination, suggesting that ''E. histolytica'' undergoes meiosis.<ref name=Kelso /> Studies of ''[[Entamoeba invadens]]'' found that, during the conversion from the [[Polyploid|tetraploid]] [[uninucleate]] [[Apicomplexan life cycle#Glossary of cell types| trophozoite]] to the tetranucleate cyst, [[homologous recombination]] is enhanced.<ref name=Singh>{{cite journal |vauthors=Singh N, Bhattacharya A, Bhattacharya S |title=Homologous recombination occurs in Entamoeba and is enhanced during growth stress and stage conversion |journal=PLOS ONE |volume=8 |issue=9 |pages=e74465 |year=2013 |pmid=24098652 |pmc=3787063 |doi=10.1371/journal.pone.0074465 |bibcode=2013PLoSO...874465S |doi-access=free }}</ref> Expression of genes with functions related to the major steps of meiotic recombination also increase during encystations.<ref name=Singh /> 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.<ref name="pmid20617172">{{cite journal |vauthors=Flowers JM, Li SI, Stathos A, Saxer G, Ostrowski EA, Queller DC, Strassmann JE, Purugganan MD |title=Variation, sex, and social cooperation: molecular population genetics of the social amoeba Dictyostelium discoideum |journal=PLOS Genet. |volume=6 |issue=7 |pages=e1001013 |year=2010 |pmid=20617172 |pmc=2895654 |doi=10.1371/journal.pgen.1001013 |doi-access=free }}</ref><ref name="pmid21929567">{{cite journal |vauthors=O'Day DH, Keszei A |title=Signalling and sex in the social amoebozoans |journal=Biol Rev Camb Philos Soc |volume=87 |issue=2 |pages=313–29 |year=2012 |pmid=21929567 |doi=10.1111/j.1469-185X.2011.00200.x |s2cid=205599638 }}</ref> Since the Amoebozoa diverged early from 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.<ref name="pmid21429931">{{cite journal |vauthors=Lahr DJ, Parfrey LW, Mitchell EA, Katz LA, Lara E |title=The chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms |journal=Proc. Biol. Sci. |volume=278 |issue=1715 |pages=2081–90 |year=2011 |pmid=21429931 |pmc=3107637 |doi=10.1098/rspb.2011.0289 }}</ref> that the majority of amoeboid lineages are anciently sexual. ==References== {{Reflist|refs= <ref name=gooday2011>{{Cite journal|last1=Gooday|first1=A. J.|last2=Aranda da Silva|first2=A.|last3=Pawlowski|first3=J.|date=2011-12-01|title=Xenophyophores (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)|journal=Deep-Sea Research Part II: Topical Studies in Oceanography|series=The Geology, Geochemistry, and Biology of Submarine Canyons West of Portugal|volume=58|issue=23–24|pages=2401–2419|doi=10.1016/j.dsr2.2011.04.005|bibcode=2011DSRII..58.2401G}}</ref> <ref name=vid2016>{{cite web |first=Aparna |last=Vidyasagar |date=April 2016 |title=What Is an Amoeba? |url=https://www.livescience.com/54281-amoeba-definition.html |website=livescience.com |access-date=8 November 2020 |language=en}}</ref> }} ==Further reading== *Walochnik, J. & Aspöck, H. (2007). [http://www.zobodat.at/pdf/DENISIA_0020_0323-0350.pdf Amöben: Paradebeispiele für Probleme der Phylogenetik, Klassifikation und Nomenklatur]. ''Denisia'' 20: 323–350. (In German) *[http://tolweb.org/notes/?note_id=51 Amoebae: Protists Which Move and Feed Using Pseudopodia] at the Tree of Life web project * Pawlowski, J. & Burki, F. (2009). [https://web.archive.org/web/20150923204916/http://www.cmde.science.ubc.ca/pdf/09PawlowskiTCS.pdf Untangling the Phylogeny of Amoeboid Protists]. ''Journal of Eukaryotic Microbiology'' 56.1: 16–25. ==External links== {{NIE Poster|Rhizopoda}} {{Commons category}} * Siemensma, F. [http://www.arcella.nl/ Microworld: world of amoeboid organisms]. * Völcker, E. & Clauß, S. [http://www.penard.de/Key/ Visual key to amoeboid morphotypes]. Penard Labs. *[https://web.archive.org/web/20090610035748/http://www.bms.ed.ac.uk/research/others/smaciver/amoebae.htm The Amoebae] website of Maciver Lab of the University of Edinburgh, brings together information from published sources. *[http://micro.magnet.fsu.edu/moviegallery/pondscum/protozoa/amoeba/index.html Molecular Expressions Digital Video Gallery: Pond Life – Amoeba (Protozoa)] – informative amoeba videos {{Protozoa protist}} {{Eukaryota classification}} {{Amoebozoa}} {{Rhizaria}} {{Excavata}} {{Authority control}} [[Category:Amoeboids|*]] [[Category:Cell biology]] [[Category:Motile cells]]'