Editing Amoeba

{{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-2008"/>

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]]''.
== Biology ==
=== Pseudopods and movement ===
[[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>

===Nutrition===
[[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}}
|-
|}

=== Sexual reproduction ===

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.

== Ecology ==

=== Pathogenic amoebae ===

[[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.

== History of knowledge and classification ==

===Conceptual origins===
[[File:Der Kleine Proteus from Roesel.jpg|thumb|250x250px|The first illustration of an amoeboid, from Rösel von Rosenhof's ''Insecten-Belustigung'' (1755)]]
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>{{cite book|last=Rösel von Rosenhof|first=August Johann|date=1755|title=Der monatlich herausgegebenen Insecten-Belustigung|trans-title=The monthly-published Insect Amusement|language=German|publication-place=Nürnberg|publisher=J.J. Fleischmann|volume=3|pages=621|url=https://books.google.com/books?id=q9JCAQAAMAAJ&pg=PA621|archive-url=https://web.archive.org/web/20150713174920/https://books.google.com/books?id=q9JCAQAAMAAJ&hl=&pg=PA621|archive-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|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 name="Dujardin-1841">{{Cite book|title=Histoire naturelle des zoophytes. Infusoires, comprenant la physiologie et la classificatin de ces animaux, et la manière de les étudier à l'aide du microscope|trans-title=Natural history of zoophytes. Infusoria, understanding the physiology and classification of these animals, and how to study them using the microscope|language=French|url=https://archive.org/details/histoirenaturelle00duja|last=Dujardin|first=Félix|publisher=Librarie Encyclopedique de Roret |date=1841 |location=Paris|doi=10.5962/bhl.title.10127}}</ref>{{rp|26}} 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-2008"/> 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|trans-title=Zoology|language=German|last=Schmarda|first=Ludwig Karl|publisher=W. Braumüller|date=1871|url=https://archive.org/details/zoologie00schmgoog/page/n173|location=Wien [Vienna]}}</ref>{{rp|156}} Later workers, including the influential taxonomist [[Otto Bütschli]], amended this group to create the class Sarcodina,<ref>{{Cite book|title=Protozoa. Abteilung 1. Sarkodina und Sporozoa|series=Dr. H.G. Bronn’s Klassen und Ordnungen des Thier-Reichs, wissenschaftlich dargestellt in Wort und Bild|language=German|volume=1|last=Bütschli|first=Otto|publisher=C. F. Winter'sche Verlagshandlung|location=Leipzig und Heidelberg|date=1880|url=https://www.biodiversitylibrary.org/page/12048011|doi=10.5962/bhl.title.11642}}</ref>{{rp|1}} a [[taxon]] that remained in wide use throughout most of the 20th century.<ref name="Page-1987"/>

=== Traditional classification ===

{{Multiple image|perrow=2|total_width=300|header=Examples of different kinds of amoebae
|image1=Amoeba proteus with many pseudopodia.jpg
|caption1=''[[Amoeba proteus]]'', a gymnamoeba
|image2=Actinophrys_sol_(phase_contrast_microscopy).jpg
|caption2=''[[Actinophrys sol]]'', a heliozoan
|image3=Naegleria_lustrarea_jeu.13031_fig1D.jpg
|caption3=''[[Naegleria lustrarea]]'', a heterolobosean
|image4=Vampyrella_lateritia.jpg
|caption4=''[[Vampyrella lateritia]]'', a proteomyxid
|image5=Collection Penard MHNG Specimen 395-3-5 Euglypha ciliata.tif
|caption5=''[[Euglypha ciliata]]'', a filose testate amoeba
|image6=Hyalosphenia papilio from Hawley Bog Massachusetts.jpg
|caption6=''[[Hyalosphenia papilio]]'', a lobose testate amoeba
|image7=Reticulomyxa filosa - Reticulopodial network.jpg
|caption7=''[[Reticulomyxa filosa]]'', a reticulose amoeba
|image8=Dictyostelium_Aggregation.JPG
|caption8=''[[Dictyostelium discoideum]]'', an eumycetozoan
}}

For convenience, all amoebae were grouped as Sarcodina and 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 '''Actinopoda''', whereas those with unsupported pseudopods were classified as '''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, plasmodial and reticulose, according to the morphology of their pseudopods. During the 1980s, taxonomists reached the following classification, based exclusively on morphological comparisons:<ref name="Levine-1980">{{cite journal|vauthors=Levine ND, Corliss JO, ((Cox FEG)), Deroux G, Grain J, Honigberg BM, Leedale GF, Loeblich AR, Lom J, Lynn D, Merinfeld EG, Page FC, Poljansky G, Sprague V, Vavra J, Wallace FG|display-authors=10|title=A newly revised classification of the Protozoa|journal=Journal of Protozoology|volume=27|issue=1|date=1980|pages=37–58|doi=10.1111/j.1550-7408.1980.tb04228.x|pmid=6989987}}</ref><ref name="Page-1987">{{cite journal|vauthors=Page FC|title=The classification of ‘naked’ amoebae (phylum Rhizopoda)|journal=Archiv für Protistenkunde|volume=133|date=1987|pages=199–217|doi=10.1016/S0003-9365(87)80053-2}}</ref>

* '''Sarcodina''' {{au|Schmarda 1871}}: all amoebae.<ref name="Levine-1980"/>{{rp|40}}

:*'''Rhizopoda''' {{au|von Siebold 1845}}: amorphous amoebae that lack axopodia and move through pseudopodia.<ref name="Levine-1980"/>{{rp|41}}<ref name="Page-1987"/>{{rp|202}}

::*[[Heterolobosea]] {{au|Page & Blanton 1985}}: amoebae with eruptive pseudopodia, similar to the lobose ones but with a distinct movement, and usually with flagellate life stages. It was traditionally divided into those which aggregate to form fruiting bodies ([[Acrasida]]) and those that do not ([[Schizopyrenida]]).<ref name="Page-1987"/>{{rp|203–204}}

::*[[Lobosea]] {{au|Carpenter 1861}}: amoebae with lobose pseudopodia. This [[paraphyletic]] group is now represented by a big portion of the current phylum [[Amoebozoa]], in particular the classes [[Tubulinea]], [[Discosea]] and [[Cutosea]].

:::*Gymnamoebia {{au|Haeckel 1862}}: lobose naked amoebae. This [[polyphyletic]] group included the classic amorphous amoebae with big, blunt pseudopodia, such as [[Euamoebida]], [[Leptomyxida]], [[Centramoebida|Acanthopodida]], [[Echinamoebida]], [[Entamoebida]], etc.

:::*Testacealobosia {{au|de Saedeleer 1934}}: lobose [[testate amoebae]]. This polyphyletic group included three unrelated lineages of amoebozoans enclosed by tests or other complex coverings: [[Arcellinida]], [[Himatismenida]] and [[Trichosida]].

::*[[Caryoblastea]] {{au|Margulis 1974}}: amoebae with sparse, non-motile flagella on the surface. This group only includes the order [[Pelobiontida]],<ref name="Page-1987"/>{{rp|207}} which now belongs to the amoebozoan group [[Archamoebae]] together with some naked amoebae.<ref name="EvoArchamoebae">{{cite journal|doi=10.1016/j.protis.2012.11.005|pmid=23312407|title=Evolution of Archamoebae: Morphological and Molecular Evidence for Pelobionts Including Rhizomastix, Entamoeba, Iodamoeba, and Endolimax|journal=Protist|volume=164|issue=3|pages=380–410|year=2013|last1=Ptáčková|first1=Eliška|last2=Kostygov|first2=Alexei Yu|last3=Chistyakova|first3=Lyudmila V|last4=Falteisek|first4=Lukáš|last5=Frolov|first5=Alexander O|last6=Patterson|first6=David J|last7=Walker|first7=Giselle|last8=Cepicka|first8=Ivan}}</ref>

::*[[Eumycetozoa|Eumycetozoea]] {{au|Zopf 1885}}: plasmodial amoebae with filiform subpseudopodia that produce fruiting bodies.

::*[[Plasmodiophorid|Plasmodiophorea]] {{au|Cook 1928}}: endoparasitic plasmodial amoebae with minute pseudopodia. This group is now an order within [[Rhizaria]], closely related to the endoparasites [[Phagomyxida]].

::*[[Filosa|Filosea]] {{au|Leidy 1879}}: amoebae with filose pseudopodia.

:::*Aconchulinia {{au|de Saedeleer 1934}}: filose naked amoebae, sometimes covered in scales. This group included two unrelated taxa: the [[nucleariid]] amoebae, closely related to [[fungi]]; and most of the [[Vampyrellida]], found in Rhizaria.

:::*Testaceafilosia {{au|de Saedeleer 1934}}: filose testate amoebae. This group included taxa now found throughout Rhizaria, such as [[Gromiida]] and [[Euglyphida]].

::*Granuloreticulosea {{au|de Saedeleer 1934}}: amoebae with delicate granular pseudopodia. This group included both the [[Foraminifera]] (now in Rhizaria) and some members of Vampyrellida.

::*[[Xenophyophorea]] {{au|Schulze 1904}}: plasmodial amoebae enclosed in a branched-tube system composed of a transparent organic substance. This group is now fully integrated into the Foraminifera.

:*'''Actinopoda''' {{au|Calkins 1909}}: spherical amoebae that float in the water column. This group included those organisms that have a [[heliozoa]]n-type appearance, with radially positioned filopodia, reticulopodia or axopodia surrounding the cell body. These were the [[Radiolaria]], [[Phaeodaria]], [[Proteomyxidea]] (all three now in Rhizaria), [[Centroplasthelida]] (now in [[Haptista]]), and [[Actinophryida]] (now in [[Stramenopiles]]).

===Transitional period===
{{cladogram|{{clade|style=line-height:90%;font-size:90%;|label1=[[Eukaryotes]]|1={{clade|1=[[Archezoa]]|2={{clade|1={{nowrap|[[Percolozoa]] (Heterolobosea)&nbsp;&nbsp;}}|barbegin1=orange|2={{clade|1=other excavates|barend1=orange|2={{clade|1='''Eosarcodina'''|state1=double|barbegin1=green|2={{clade|1='''Neosarcodina'''|state1=double|barend1=green|2={{clade|1=[[Apusozoa]] → [[Choanozoa]] → [[Animals]], [[Fungi]]|2='''Actinopoda'''|3=[[Alveolata]] → [[Plants]], [[Chromista]]}}}}}}}}}}}}
|grouplabel1={{clade labels|label1=[[Excavata|Eozoa]]|top1=17%|label2='''Sarcodina'''|top2=40%}}
}}
|caption=The 'amoeboflagellate' hypothesis by [[Thomas Cavalier-Smith]], where higher eukaryotes evolved from amoeboid phyla.<ref name="Cavalier-Smith-1997"/>{{rp|244}}
}}
In the final decades of the 20th century, a series of molecular phylogenetic analyses confirmed that Sarcodina was not a [[monophyletic]] group, and that amoebae evolved from flagellate ancestors.<ref name="Pawlowski-2008"/> The protozoologist [[Thomas Cavalier-Smith]] proposed that the ancestor of most eukaryotes was an [[amoeboflagellate]] much like modern [[heterolobosea]]ns, which in turn  gave rise to a paraphyletic Sarcodina from which other groups (e.g., alveolates, animals, plants) evolved by 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).<ref name="Cavalier-Smith-1997">{{cite journal|last1=Cavalier-Smith|first1=Thomas|title=Amoeboflagellates and Mitochondrial Cristae in Eukaryote Evolution: Megasystematics of the New Protozoan Subkingdoms Eozoa and Neozoa|journal=Archiv für Protistenkunde|date=1996–1997|volume=147|issue=3–4|pages=237–258|doi=10.1016/S0003-9365(97)80051-6}}</ref>

Shortly after, phylogenetic analyses disproved this hypothesis, as non-amoeboid [[zooflagellate]]s and amoeboflagellates were found to be completely intermingled with amoebae. With 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.<ref name="Cavalier-Smith-1998">{{cite journal|title=A revised six-kingdom system of life|last1=Cavalier-Smith|first1=Thomas|journal=Biological Reviews|doi=10.1111/j.1469-185X.1998.tb00030.x|volume=73|issue=3|pages=203–266|date=1998}}</ref>{{rp|238}} The phylum Amoebozoa was conserved, as it still primarily included amoeboid organisms, and now included the Mycetozoa.<ref name="Cavalier-Smith-1998"/>{{rp|232}}

=== Current classification ===

Today, amoebae are dispersed among many high-level taxonomic groups. The majority of traditional sarcodines are placed in two eukaryote [[Supergroup (biology)|supergroups]]: [[Amoebozoa]] and [[Rhizaria]]. The rest have been distributed among the [[Excavata|excavates]], [[opisthokonts]], [[stramenopiles]] and minor clades.<ref name="Pawlowski-2008"/><ref name="Adl 2012">{{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>

* [[Amoebozoa]] {{au|Lühe 1913 em. Cavalier-Smith 1998}}: includes all naked and testate lobose amoebae (traditional Lobosea) as well as the [[pelobiont]]s and [[eumycetozoa]]ns, and a few flagellates.<ref name="Pawlowski-2009"/>{{rp|17}}

* [[Rhizaria]] {{au|Cavalier-Smith 2002}}: includes amoebae bearing reticulose or filose pseudopodia, the majority of which were traditionally classified as Filosea, Granuloreticulosea and Actinopoda, such as [[Euglyphida]], [[Gromiida]], [[Radiolaria]], [[Proteomyxidea]], [[Phaeodarea]] and [[Foraminifera]] (including [[Xenophyophorea]]). It also houses a large diversity of free-living flagellates, amoeboflagellates and parasites like the [[Plasmodiophorida]].<ref name="Pawlowski-2009"/>{{rp|17}}

* [[Heterolobosea]] {{au|Page & Blanton 1985}}: amoebae with lobose pseudopodia but eruptive flow of cytoplasm. Currently it includes the aggregative Acrasida, as well as several other amoeboflagellates. They are a class of [[excavata|excavate]]s closely related to [[Euglenozoa]], with whom they share their characteristic discoidal [[crista|mitochondrial cristae]].<ref name="Pawlowski-2008"/>{{rp|293}}

* [[Stramenopiles]] {{au|Patterson 1989 em. Adl et al. 2005}}: although primarily composed by flagellates, it contains a few groups of amoebae. For example: the [[Actinophryida]], an order with typical heliozoan morphology;<ref name="Pawlowski-2008"/>{{rp|293}} the amoeboid ''[[Rhizochromulina]]'', a genus of [[chrysophyte]]s;<ref name="Hibberd-2009"/> or ''[[Synchroma]]'', a genus of amoeboid algae with reticulate axopodia.<ref name="Horn-2007"/>

* [[Nucleariid|Rotosphaerida]] {{au|Rainer 1968}}: also known as [[nucleariid]]s, includes a few filose amoebae traditionally classified within the Filosea, positioned as the sister group of [[Fungi]].<ref name="Gabaldón-2022"/>

* [[Centroplasthelida]] {{au|Febvre-Chevalier & Febvre 1984}}: heliozoans with a centroplast from which axopodia arise.<ref name="Pawlowski-2008"/>{{rp|293}} They are closely related to the [[haptophyte]] algae inside the supergroup [[Haptista]].<ref name="Burki-2016"/>

* [[Rigifilida]] {{au|Cavalier-Smith 2012}}: a small order of filose amoebae previously interpreted as nucleariids.<ref name="Yabuki-2012"/> Together with the flagellate orders [[Mantamonadida]] and [[Diphylleida]], it composes the [[CRuMs]] clade, positioned closest to [[Amorphea]].<ref name="Brown-2018"/>

* [[Breviatea]] {{au|Cavalier-Smith 2004}}: includes enigmatic free-living [[amoeboflagellate]]s related to [[opisthokont]]s.<ref name="Brown-2013"/>

The following cladogram shows the sparse positions of amoeboid groups (in bold), based on molecular phylogenetic analyses:<ref name="Brown-2018"/>
{{clade|label1=[[Eukaryotes]]|style=font-size:90%;line-height:90%;|1={{clade
 |label1=[[Diaphoretickes]]|1={{clade
  |1={{clade
   |label2=[[Haptista]]|2={{clade
    |1=[[haptophyte]]s
    |2='''[[Centroplasthelida]]'''
    }}
   |label1=[[SAR supergroup|SAR]]|1={{clade
    |1='''[[Stramenopiles]]'''
    |3='''[[Rhizaria]]'''
    |2=[[alveolate]]s
    }}
   }}
  |2=[[plants]], etc.
  }}
 |label2=[[Discoba]]|2={{clade
  |1=[[euglenid]]s, etc.
  |2='''[[Heterolobosea]]'''
  }}
 |label3=[[Podiata]]|3={{clade
  |1=[[CRuMs]] (incl. '''[[Rigifilida]]''')
  |label2=[[Amorphea]]|2={{clade
   |1='''[[Amoebozoa]]'''
   |label2=[[Obazoa]]|2={{clade
    |1='''[[Breviatea]]'''
   |2={{clade
    |1=[[apusomonad]]s
    |label2=[[Opisthokonta]]
    |2={{clade
     |label1=[[Holomycota]]|1={{clade
      |1='''[[Nucleariid]]s'''
      |2=[[Fungi]]
      }}
   |label2=[[Holozoa]]|2=[[animal]]s, etc.}}
  }}
 }}
}}
}}
}}
}}

==Amoeboid cells in other organisms==
[[File:Neutrophil with anthrax copy.jpg|thumb|[[Neutrophil]] (white blood cell) engulfing anthrax bacteria]]
===Amoeboid cell types in multicellular organisms===
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> [[Sponge]]s exhibit a [[totipotent]] cell type known as [[archaeocyte]]s, capable of transforming into the feeding cells or [[choanocyte]]s.<ref>{{cite journal|first1=Maja|last1=Adamska|title=Sponges as models to study emergence of complex animals|journal=Current Opinion in Genetics & Development|volume=39|date=August 2016|pages=21–28|doi=10.1016/j.gde.2016.05.026}}</ref>
===Amoeboid dispersal stages===
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}}

==References==

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==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)

==External links==

{{NIE Poster|Rhizopoda}}
{{Commons category}}
* [http://tolweb.org/notes/?note_id=51 Amoebae: Protists Which Move and Feed Using Pseudopodia] at the Tree of Life web project
* 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]]
[[Category:Microbiology]]
[[Category:Microorganisms]]
[[Category:Eukaryote morphology]]
[[Category:Protista]]