Editing Zooplankton (section)

==Taxonomic groups==
===Protozoans===
{{further|marine protists#Protozoans}}

[[Protozoan]]s are [[protist]]s that feed on organic matter such as other [[microorganism]]s or organic tissues and debris.<ref>{{Cite book |url=https://books.google.com/books?id=sYgKY6zz20YC&q=panno+the+cell&pg=PA130 |title=The Cell: Evolution of the First Organism |last=Panno |first=Joseph |date=14 May 2014 |publisher=Infobase Publishing |isbn=9780816067367 |language=en}}</ref><ref>{{Cite book |url=https://books.google.com/books?id=2zVqBgAAQBAJ&q=endocytosis&pg=PA9 |title=Environmental Microbiology: Fundamentals and Applications: Microbial Ecology |last1=Bertrand |first1=Jean-Claude |last2=Caumette |first2=Pierre |last3=Lebaron |first3=Philippe |last4=Matheron |first4=Robert |last5=Normand |first5=Philippe |last6=Sime-Ngando |first6=Télesphore |date=2015-01-26 |publisher=Springer |isbn=9789401791182 |language=en}}</ref> Historically, the protozoa were regarded as "one-celled animals", because they often possess [[animal]]-like behaviours, such as [[motility]] and [[predation]], and lack a [[cell wall]], as found in plants and many [[algae]].<ref>{{Cite book|url=https://books.google.com/books?id=RawZTwEACAAJ&q=brock+biology+of+microorganisms+13th|title=Brock Biology of Microorganisms |last=Madigan |first=Michael T. |date=2012 |publisher=Benjamin Cummings |isbn=9780321649638}}</ref><ref>{{Cite book |url=https://www.ncbi.nlm.nih.gov/books/NBK8325/ |title=Protozoa: Structure, Classification, Growth, and Development |last=Yaeger |first=Robert G. |date=1996 |publisher=NCBI |pmid=21413323 |access-date=2018-03-23 |isbn=9780963117212 }}</ref> Although the traditional practice of grouping protozoa with animals is no longer considered valid, the term continues to be used in a loose way to identify single-celled organisms that can move independently and feed by [[heterotroph]]y.

Marine protozoans include [[zooflagellate]]s, [[foraminifera]]ns, [[radiolarian]]s and some [[dinoflagellate]]s.

====Radiolarians====
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  | footer            = &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Drawings by [[Ernst Haeckel|Haeckel]] 1904 (click for details)
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[[Radiolarian]]s are unicellular predatory [[#Marine protists|protists]] encased in elaborate globular shells usually made of silica and pierced with holes. Their name comes from the Latin for "radius". They catch prey by extending parts of their body through the holes. As with the silica frustules of diatoms, radiolarian shells can sink to the ocean floor when radiolarians die and become preserved as part of the [[ocean sediment]]. These remains, as [[#Marine microfossils|microfossils]], provide valuable information about past oceanic conditions.<ref name=Wassilieff2006b>Wassilieff, Maggy (2006) [http://www.TeAra.govt.nz/en/photograph/5138/radiolarian-fossils "Plankton – Animal plankton"], ''Te Ara – the Encyclopedia of New Zealand''. Accessed: 2 November 2019.</ref>

<gallery mode="packed" heights="150px" style="float:left;">
File:Mikrofoto.de-Radiolarien 6.jpg|Like diatoms, radiolarians come in many shapes
File:Podocyrtis papalis Ehrenberg - Radiolarian (30448963206).jpg|Also like diatoms, radiolarian shells are usually made of silicate
File:Acantharian radiolarian Xiphacantha (Haeckel).jpg|However [[acantharian]] radiolarians have shells made from [[strontium sulfate]] crystals
File:Spherical radiolarian 2.jpg|Cutaway schematic diagram of a spherical radiolarian shell
</gallery>

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| video1 = [https://www.youtube.com/watch?v=5rxwn6vT9JE Radiolarian geometry]
| video2 = [https://www.youtube.com/watch?v=tl_onFMjJWA Ernst Haeckel's radiolarian engravings]
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====Foraminiferans====
Like radiolarians, [[foraminifera]]ns (''forams'' for short) are single-celled predatory protists, also protected with shells that have holes in them. Their name comes from the Latin for "hole bearers". Their shells, often called [[Test (biology)|tests]], are chambered (forams add more chambers as they grow). The shells are usually made of calcite, but are sometimes made of [[Agglutination (biology)|agglutinated]] sediment particles or [[chiton]], and (rarely) silica. Most forams are benthic, but about 40 species are planktic.<ref name=Hemleben>{{cite book |first1=C. |last1=Hemleben |first2=O.R. |last2=Anderson |first3=M. |last3=Spindler |title=Modern Planktonic Foraminifera |url=https://books.google.com/books?id=NaHOmAEACAAJ |year=1989 |publisher=Springer-Verlag |isbn=978-3-540-96815-3}}</ref> They are widely researched with well-established fossil records which allow scientists to infer a lot about past environments and climates.<ref name=Wassilieff2006b />

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 | footer            = Foraminiferans are important unicellular zooplankton [[#Marine protists|protists]], with calcium tests
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 | image1    = Foram-globigerina hg.jpg
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 | caption1  = ...can have more than one nucleus
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 | caption2  = ...and defensive spines
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<gallery mode="packed" heights="144px" style="float:left;">
File:EB1911 Foraminifera - Section of Rotalia beccarii.jpg|section showing chambers of a spiral foram
File:Live Ammonia tepida.jpg|Live ''[[Ammonia tepida]]'' streaming granular ectoplasm for catching food
File:Planktic Foraminifera of the northern Gulf of Mexico.jpg|Group of planktonic forams
File:All Gizah Pyramids.jpg|The [[Egyptian pyramid]]s were constructed from limestone that contained [[nummulite]]s.<ref>[http://www.ucl.ac.uk/GeolSci/micropal/foram.html#histofstudy Foraminifera: History of Study], [[University College London]]. Retrieved: 18 November 2019.</ref>
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| video1 = [https://www.youtube.com/watch?v=JLSa8cGJixQ foraminiferans]
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====Amoeba====
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  | footer            = &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; [[Amoeba]] can be shelled ([[testate]]) or naked
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  | image1    = Cyphoderia ampulla - Testate amoeba - 160x (14997391862).jpg
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  | caption1  = [[Testate amoeba]], ''[[Cyphoderia]]'' sp.
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  | caption2  = {{center|Naked amoeba, ''[[Chaos carolinensis]]''}}
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<gallery mode="packed" heights="170px" style="float:left;">
File:Amoeba proteus 2.jpg|Naked amoeba sketch showing food vacuoles and ingested diatom
File:Arcella sp.jpg|Shell or test of a [[testate amoeba]], ''[[Arcella]]'' sp.
File:Collection Penard MHNG Specimen 533-2-1 Pamphagus granulatus.tif|[[wiktionary:xenogenic|Xenogenic]] testate amoeba covered in diatoms 
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====Ciliates====
<gallery mode="packed" heights="150px" style="float:left;">
File:Stylonychia putrina - 160x - II (13215594964).jpg|''[[Stylonychia|Stylonychia putrina]]''
File:Holophyra ovum - 400x (9836710085).jpg|''Holophyra'' ovum
File:Mikrofoto.de-Blepharisma japonicum 15.jpg|''[[Blepharisma japonicum]]''
File:The ciliate Frontonia sp.jpg|This [[ciliate]] is digesting [[cyanobacteria]]. The mouth is at the bottom right.
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====Dinoflagellates====
{{see also|Predatory dinoflagellate}}

[[Dinoflagellate]]s are a phylum of unicellular [[flagellate]]s with about 2,000 marine species.<ref name="Gómez12">{{cite journal|author=Gómez F |title=A checklist and classification of living dinoflagellates (Dinoflagellata, Alveolata) |journal=CICIMAR Oceánides |volume=27 |issue=1 |pages=65–140 |year=2012 |doi=10.37543/oceanides.v27i1.111 |doi-access=free }}</ref> Some dinoflagellates are [[Predatory dinoflagellate|predatory]], and thus belong to the zooplankton community. Their name comes from the Greek "dinos" meaning ''whirling'' and the Latin "flagellum" meaning a ''whip'' or ''lash''. This refers to the two whip-like attachments (flagella) used for forward movement. Most dinoflagellates are protected with red-brown, cellulose armour. [[Excavata|Excavates]] may be the most basal flagellate lineage.<ref name=Dawson2013>{{cite journal |last1=Dawson |first1=Scott C |last2=Paredez |first2=Alexander R |title=Alternative cytoskeletal landscapes: cytoskeletal novelty and evolution in basal excavate protists |journal=Current Opinion in Cell Biology |year=2013 |volume=25 |issue=1 |pages=134–141 |doi=10.1016/j.ceb.2012.11.005 |pmid=23312067 |pmc=4927265}}</ref>

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 | image1    = Peridinium digitale.jpg
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 | caption1  = &nbsp; &nbsp; &nbsp; &nbsp; Armoured
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<gallery mode="packed" heights="144px" style="float:right;">
File:Gyrodinium dinoflagellate.jpg|''[[Gymnodinium|Gyrodinium]]'', one of the few naked dinoflagellates which lack armour
File:Protoperidinium dinoflagellate.jpg|The dinoflagellate ''Protoperidinium'' extrudes a large feeding veil to capture prey
File:Radiolarian - Podocyrtis (Lampterium) mitra Ehrenberg - 160x.jpg|[[Nassellarian]] radiolarians can be in symbiosis with dinoflagellates
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Dinoflagellates often live in [[symbiosis]] with other organisms. Many [[nassellarian]] radiolarians house [[dinoflagellate]] [[Symbiosis|symbionts]] within their tests.<ref>{{Cite book |title=Handbook of the Protists |last1=Boltovskoy |first1=Demetrio |last2=Anderson |first2=O. Roger |last3=Correa |first3=Nancy M. |date=2017 |publisher=Springer, Cham |isbn=9783319281476 |pages=731–763 |language=en |doi=10.1007/978-3-319-28149-0_19}}</ref> The nassellarian provides [[ammonium]] and [[carbon dioxide]] for the dinoflagellate, while the dinoflagellate provides the nassellarian with a mucous membrane useful for hunting and protection against harmful invaders.<ref>{{Cite book |title=Radiolaria |last=Anderson |first=O. R. |publisher=Springer Science & Business Media |year=1983}}</ref> There is evidence from [[DNA]] analysis that dinoflagellate symbiosis with radiolarians evolved independently from other dinoflagellate symbioses, such as with [[foraminifera]].<ref>{{Cite journal |last1=Gast |first1=R. J. |last2=Caron |first2=D. A. |date=1996-11-01 |title=Molecular phylogeny of symbiotic dinoflagellates from planktonic foraminifera and radiolaria |journal=Molecular Biology and Evolution |language=en |volume=13 |issue=9 |pages=1192–1197 |doi=10.1093/oxfordjournals.molbev.a025684 |pmid=8896371 |issn=0737-4038 |doi-access=}}</ref>

<gallery mode="packed" heights="144px" style="float:left;">
File:Ceratium tripos.jpg|[[Tripos (dinoflagellate)|''Tripos muelleri'']] is recognisable by its U-shaped horns
File:Archives de zoologie expérimentale et générale (1920) (20299351186).jpg|''[[Oodinium]]'', a genus of [[parasitic]] dinoflagellates, causes [[velvet disease]] in fish<ref>{{cite web|title=Protozoa Infecting Gills and Skin|url=http://www.merckvetmanual.com:80/mvm/index.jsp?cfile=htm/bc/170410.htm|publisher=[[The Merck Veterinary Manual]]|access-date= 4 November 2019|archive-url=https://web.archive.org/web/20160303221140/http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm%2Fbc%2F170410.htm|archive-date=3 March 2016|url-status=dead|df=dmy-all}}</ref>
File:Karenia brevis.jpg|''[[Karenia brevis]]'' produces red tides highly toxic to humans<ref>{{Cite journal|last1=Brand|first1=Larry E.|last2=Campbell|first2=Lisa|last3=Bresnan|first3=Eileen|title=''Karenia'': The biology and ecology of a toxic genus|journal=Harmful Algae|volume=14|pages=156–178|doi=10.1016/j.hal.2011.10.020|year=2012|pmid=36733478 |pmc=9891709 |bibcode=2012HAlga..14..156B }}</ref>
File:Algal bloom(akasio) by Noctiluca in Nagasaki.jpg|[[Red tide]]
</gallery>

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===Mixotrophs===
{{see also|Mixotroph|Mixotrophic dinoflagellate}}

A [[mixotroph]] is an organism that can use a mix of different [[Primary nutritional groups|sources of energy and carbon]], instead of having a single trophic mode on the continuum from complete [[autotrophy]] at one end to [[heterotrophy]] at the other. It is estimated that mixotrophs comprise more than half of all microscopic plankton.<ref>{{Cite web |last=Collins |first=Richard |date=2016-11-14 |title=Beware the mixotrophs – they can destroy entire ecosystems 'in a matter of hours' |url=https://www.irishexaminer.com/opinion/columnists/arid-20430358.html |website=Irish Examiner |language=en}}</ref> There are two types of eukaryotic mixotrophs: those with their own [[chloroplast]]s, and those with [[endosymbiont]]s—and others that acquire them through [[kleptoplasty]] or by enslaving the entire phototrophic cell.<ref>{{Cite web |last=University |first=Swansea |title=Microscopic body snatchers infest our oceans |url=https://phys.org/news/2017-08-microscopic-body-snatchers-infest-oceans.html |website=phys.org |language=en}}</ref>

The distinction between plants and animals often breaks down in very small organisms. Possible combinations are [[phototroph|photo-]] and [[chemotroph]]y, [[lithotroph|litho-]] and [[organotroph]]y, [[autotroph|auto-]] and [[heterotroph]]y or other combinations of these. Mixotrophs can be either [[eukaryote|eukaryotic]] or [[prokaryote|prokaryotic]].<ref name='Eiler'>{{cite journal |author=Eiler A |title=Evidence for the Ubiquity of Mixotrophic Bacteria in the Upper Ocean: Implications and Consequences |journal=Appl Environ Microbiol |volume=72 |issue=12 |pages=7431–7 |date=December 2006 |pmid=17028233 |doi=10.1128/AEM.01559-06 |pmc=1694265 |bibcode=2006ApEnM..72.7431E }}</ref> They can take advantage of different environmental conditions.<ref>{{cite journal |vauthors=Katechakis A, Stibor H |title=The mixotroph ''Ochromonas tuberculata'' may invade and suppress specialist phago- and phototroph plankton communities depending on nutrient conditions |journal=Oecologia |volume=148 |issue=4 |pages=692–701 |date=July 2006 |pmid=16568278 |doi=10.1007/s00442-006-0413-4 |bibcode=2006Oecol.148..692K |s2cid=22837754 }}</ref>

Many marine microzooplankton are mixotrophic, which means they could also be classified as phytoplankton. Recent studies of marine microzooplankton found 30–45% of the ciliate abundance was mixotrophic, and up to 65% of the amoeboid, foram and radiolarian [[Biomass (ecology)|biomass]] was mixotrophic.<ref name=Leles2017>{{cite journal | last1 = Leles | first1 = S.G. | last2 = Mitra | first2 = A. | last3 = Flynn | first3 = K.J. | last4 = Stoecker | first4 = D.K. | last5 = Hansen | first5 = P.J. | last6 = Calbet | first6 = A. | last7 = McManus | first7 = G.B. | last8 = Sanders | first8 = R.W. | last9 = Caron | first9 = D.A. | last10 = Not | first10 = F. | last11 = Hallegraeff | first11 = G.M. | year = 2017 | title = Oceanic protists with different forms of acquired phototrophy display contrasting biogeographies and abundance | journal = Proceedings of the Royal Society B: Biological Sciences | volume = 284 | issue = 1860| page = 20170664 | doi = 10.1098/rspb.2017.0664 | pmid = 28768886 | pmc = 5563798 }}</ref>

{|class="wikitable"
! colspan=7 |{{centre|Mixotrophic zooplankton that combine phototrophy and heterotrophy – table based on Stoecker et al., 2017 <ref  name=Stoecker2017>{{cite journal | last1 = Stoecker | first1 = D.K. | last2 = Hansen | first2 = P.J. | last3 = Caron | first3 = D.A. | last4 = Mitra | first4 = A. | year = 2017 | title = Mixotrophy in the marine plankton | url = http://pdfs.semanticscholar.org/8492/ec7724a468af240e014aa539a8865568473d.pdf | archive-url = https://web.archive.org/web/20190227180157/http://pdfs.semanticscholar.org/8492/ec7724a468af240e014aa539a8865568473d.pdf | url-status = dead | archive-date = 2019-02-27 | journal = Annual Review of Marine Science | volume = 9 | pages = 311–335 | doi = 10.1146/annurev-marine-010816-060617 | pmid = 27483121 | bibcode = 2017ARMS....9..311S | s2cid = 25579538 }}</ref>}}
|-
! colspan=2 | Description
! colspan=2 | Example
! Further examples
|-
| colspan=5 | Called '''''nonconstitutive mixotrophs''''' by Mitra et al., 2016.<ref name=Mitra2016>{{cite journal | last1 = Mitra | first1 = A | last2 = Flynn | first2 = KJ | last3 = Tillmann | first3 = U | last4 = Raven | first4 = J | last5 = Caron | first5 = D | display-authors = etal | year = 2016 | title = Defining planktonic protist functional groups on mechanisms for energy and nutrient acquisition; incorporation of diverse mixotrophic strategies | journal = Protist | volume = 167 | issue = 2| pages = 106–20 | doi = 10.1016/j.protis.2016.01.003 | pmid = 26927496 | doi-access = free | hdl = 10261/131722 | hdl-access = free }}</ref> Zooplankton that are photosynthetic: microzooplankton or metazoan zooplankton that acquire phototrophy through chloroplast retention<sup>a</sup> or maintenance of algal endosymbionts.
|-
| Generalists  
| Protists that retain chloroplasts and rarely other organelles from many algal taxa
| [[File:Halteria.jpg|100px]]
| 
| Most [[oligotrich]] ciliates that retain plastids<sup>a</sup>
|-
| rowspan=2 | Specialists
| 1. Protists that retain chloroplasts and sometimes other organelles from one algal species or very closely related algal species
| [[File:Dinophysis acuminata.jpg|100px]]
| ''[[Dinophysis acuminata]]''
|  ''[[Dinophysis]]'' spp.<br />''[[Myrionecta rubra]]''
|-
| 2. Protists or zooplankton with algal endosymbionts of only one algal species or very closely related algal species
| [[File:Noctiluca scintillans varias.jpg|100px]]
| ''[[Noctiluca scintillans]]''
|  [[wiktionary:metazooplankton|Metazooplankton]] with algal [[endosymbiont]]s<br />Most mixotrophic [[Rhizaria]] ([[Acantharea]], [[Polycystinea]], and [[Foraminifera]])<br />Green ''[[Noctiluca scintillans]]''
|-
| colspan=7 style="text-align:center;" | <small><sup>a</sup>Chloroplast (or plastid) retention = sequestration = enslavement. Some plastid-retaining species also retain other organelles and prey cytoplasm.</small>
|}

''Phaeocystis'' species are endosymbionts to [[Acantharea|acantharian]] radiolarians.<ref name=":4">{{cite journal |last1=Decelle |first1=Johan |last2=Simó |first2=Rafel |last3=Galí |first3=Martí |last4=Vargas |first4=Colomban de |last5=Colin |first5=Sébastien |last6=Desdevises |first6=Yves |last7=Bittner |first7=Lucie |last8=Probert |first8=Ian |last9=Not |first9=Fabrice |date=2012-10-30 |title=An original mode of symbiosis in open ocean plankton |journal=Proceedings of the National Academy of Sciences |language=en |volume=109 |issue=44 |pages=18000–18005 |doi=10.1073/pnas.1212303109 |issn=0027-8424 |pmid=23071304 |pmc=3497740 |bibcode=2012PNAS..10918000D |doi-access=free}}</ref><ref name=":5">{{Cite journal |last1=Mars Brisbin |first1=Margaret |last2=Grossmann |first2=Mary M. |last3=Mesrop |first3=Lisa Y. |last4=Mitarai |first4=Satoshi |date=2018 |title=Intra-host Symbiont Diversity and Extended Symbiont Maintenance in Photosymbiotic Acantharea (Clade F) |journal=Frontiers in Microbiology |language=en |volume=9 |pages=1998 |doi=10.3389/fmicb.2018.01998 |pmid=30210473 |pmc=6120437 |issn=1664-302X |doi-access=free}}</ref> ''[[Phaeocystis]]'' is an important algal genus found as part of the marine [[phytoplankton]] around the world. It has a [[Polymorphism (biology)|polymorphic]] life cycle, ranging from free-living cells to large colonies.<ref name=":0">{{Cite journal|title = Phaeocystis blooms in the global ocean and their controlling mechanisms: a review|journal = Journal of Sea Research|date = 2005-01-01|pages = 43–66|volume = 53|series = Iron Resources and Oceanic Nutrients – Advancement of Global Environmental Simulations|issue = 1–2|doi = 10.1016/j.seares.2004.01.008|first1 = Véronique|last1 = Schoemann|first2 = Sylvie|last2 = Becquevort|first3 = Jacqueline|last3 = Stefels|first4 = Véronique|last4 = Rousseau|first5 = Christiane|last5 = Lancelot|citeseerx = 10.1.1.319.9563|bibcode = 2005JSR....53...43S}}</ref> It has the ability to form floating colonies, where hundreds of cells are embedded in a gel matrix, which can increase massively in size during [[Algal bloom|blooms]].<ref>{{cite web |url=http://www.phaeocystis.org/ |title=Welcome to the Phaeocystis antarctica genome sequencing project homepage |access-date=2020-08-23 |archive-date=2015-11-20 |archive-url=https://web.archive.org/web/20151120043948/http://www.phaeocystis.org/ |url-status=dead }}</ref> As a result, ''Phaeocystis'' is an important contributor to the marine [[Carbon cycle|carbon]]<ref>{{cite journal |title=Rapid and early export of Phaeocystis antarctica blooms in the Ross Sea, Antarctica <!--http://www.nature.com/doifinder/10.1038/35007061-->|journal = Nature|pages = 595–598|volume = 404|issue = 6778|doi = 10.1038/35007061|pmid = 10766240|first1 = G. R.|last1 = DiTullio|first2 = J. M.|last2 = Grebmeier|author-link2=Jacqueline M. Grebmeier|first3 = K. R.|last3 = Arrigo|first4 = M. P.|last4 = Lizotte|first5 = D. H.|last5 = Robinson|first6 = A.|last6 = Leventer|first7 = J. P.|last7 = Barry|first8 = M. L.|last8 = VanWoert|first9 = R. B.|last9 = Dunbar|year = 2000|bibcode = 2000Natur.404..595D|s2cid = 4409009}}</ref> and [[sulfur cycle]]s.<ref>{{Cite journal|title = DMSP-lyase activity in a spring phytoplankton bloom off the Dutch coast, related to Phaeocystis sp. abundance|journal = Marine Ecology Progress Series|date = 1995-07-20|pages = 235–243|volume = 123|doi = 10.3354/meps123235|first1 = Stefels|last1 = J|first2 = Dijkhuizen|last2 = L|first3 = Gieskes|last3 = WWC|url = https://pure.rug.nl/ws/files/62552225/DMSP_lyase_activity_in_a_spring_phytoplankton_bloom_off_the_Dutch_coast.pdf|bibcode = 1995MEPS..123..235S|doi-access = free}}</ref>

<gallery caption="Mixoplankton" mode="packed" heights="144px" style="float:left;">
File:Tintinnid ciliate Favella.jpg|[[Tintinnid]] ciliate ''Favella''
File:Euglena mutabilis - 400x - 1 (10388739803) (cropped).jpg|''[[Euglena|Euglena mutabilis]]'', a photosynthetic [[flagellate]]
File:Stichotricha secunda - 400x (14974779356).jpg|[[Zoochlorellae]] (green) living inside the [[ciliate]] ''Stichotricha secunda''
File:Dinophysis acuta.jpg| The dinoflagellate ''Dinophysis acuta''
</gallery>

{{multiple image
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 | caption2  = White ''Phaeocystis'' algal foam washing up on a beach
}}

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A number of forams are mixotrophic. These have unicellular [[algae]] as [[endosymbiont]]s, from diverse lineages such as the [[green algae]], [[red algae]], [[golden algae]], [[diatom]]s, and [[dinoflagellate]]s.<ref name=Hemleben/> Mixotrophic foraminifers are particularly common in nutrient-poor oceanic waters.<ref>{{Cite book |last=Marshall |first=K. C. |url=https://books.google.com/books?id=QvvlBwAAQBAJ&dq=%22The+symbiont-bearing+foraminifera+are+particularly+common+in+nutrient-poor+oceanic+waters%22&pg=PA22 |title=Advances in Microbial Ecology |date=2013-11-11 |publisher=Springer Science & Business Media |isbn=978-1-4684-7612-5 |language=en}}</ref> Some forams are [[kleptoplasty|kleptoplastic]], retaining [[chloroplast]]s from ingested algae to conduct [[photosynthesis]].<ref>{{Cite journal|title = Benthic Foraminifera of dysoxic sediments: chloroplast sequestration and functional morphology|year = 1999|last= Bernhard|first=J. M.|author2=Bowser, S.M.|journal = Earth-Science Reviews|volume = 46|issue = 1|pages = 149–165|doi = 10.1016/S0012-8252(99)00017-3|bibcode=1999ESRv...46..149B}}</ref>

By trophic orientation, dinoflagellates are all over the place. Some dinoflagellates are known to be [[photosynthesis|photosynthetic]], but a large fraction of these are in fact [[mixotrophy|mixotrophic]], combining photosynthesis with ingestion of prey ([[phagotrophy]]).<ref>{{Cite journal | last1 = Stoecker | first1 = D. K. | title = Mixotrophy among Dinoflagellates | doi = 10.1111/j.1550-7408.1999.tb04619.x | journal = The Journal of Eukaryotic Microbiology | volume = 46 | issue = 4 | pages = 397–401 | year = 1999 | s2cid = 83885629 | name-list-style = vanc}}</ref> Some species are [[endosymbiont]]s of marine animals and other protists, and play an important part in the biology of [[coral reef]]s. Others predate other protozoa, and a few forms are parasitic. Many dinoflagellates are [[mixotrophic]] and could also be classified as phytoplankton. The toxic dinoflagellate ''[[Dinophysis acuta]]'' acquire chloroplasts from its prey. "It cannot catch the cryptophytes by itself, and instead relies on ingesting ciliates such as the red ''[[Myrionecta rubra]]'', which sequester their chloroplasts from a specific cryptophyte clade (Geminigera/Plagioselmis/Teleaulax)".<ref  name=Stoecker2017 />

===Metazoa (animals)===
[[File:Fish3562 - Flickr - NOAA Photo Library.jpg|thumb|{{center|Octopus larva and pteropod}}]]

Free-living species in the crustacean class [[Copepod]]a are typically 1 to 2&nbsp;mm long with teardrop-shaped bodies. Like all crustaceans, their bodies are divided into three sections: head, thorax, and abdomen, with two pairs of antennae; the first pair is often long and prominent. They have a tough [[exoskeleton]] made of calcium carbonate and usually have a [[Crustacean larva#Nauplius|single red eye]] in the centre of their transparent head.<ref name=IZ>{{cite book |author=Robert D. Barnes |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location=[[Philadelphia, Pennsylvania]] |pages=683–692 |isbn=978-0-03-056747-6}}</ref> About 13,000 species of copepods are known, of which about 10,200 are marine.<ref>{{Cite web |url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=1080 |title=WoRMS - World Register of Marine Species - Copepoda |website=www.marinespecies.org |access-date=2019-06-28 |archive-url=https://web.archive.org/web/20190630192104/http://www.marinespecies.org/aphia.php?p=taxdetails&id=1080 |archive-date=2019-06-30 |url-status=live}}</ref><ref>{{cite journal |author1=Geoff A. Boxhall |author2=Danielle Defaye |year=2008 |title=Global diversity of copepods (Crustacea: Copepoda) in freshwater |journal=[[Hydrobiologia]] |volume=595 |issue=1 |pages=195–207 |doi=10.1007/s10750-007-9014-4 |s2cid=31727589 }}</ref> They are usually among the more dominant members of the zooplankton.<ref>{{cite web |author1=Johannes Dürbaum |author2=Thorsten Künnemann |date=November 5, 1997 |title=Biology of Copepods: An Introduction |url=http://www.uni-oldenburg.de/zoomorphology/Biologyintro.html |publisher=[[Carl von Ossietzky University of Oldenburg]] |access-date=December 8, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100526164720/http://www.uni-oldenburg.de/zoomorphology/Biologyintro.html |archive-date=May 26, 2010 }}</ref>

In addition to copepods the crustacean classes [[ostracod]]s, [[Branchiopoda|branchiopods]] and [[malacostraca]]ns also have planktonic members. [[Barnacle]]s are planktonic only during the larval stage.<ref>[https://books.google.com/books?id=5kv3AwAAQBAJ&dq=pelagic+realm+significant+crustaceans+pelagic+fauna+Ostracoda+Copepoda&pg=PA25 Treatise on Zoology – Anatomy, Taxonomy, Biology. The Crustacea]</ref>

<gallery mode="packed" heights="120px" caption="[[Metazoan]] zooplankton" style="float:left">
File:Copepod 2 with eggs.jpg| [[Copepod]] with eggs
File:Tomopteriskils.jpg|[[Segmented worm]]
File:Hyperia.jpg| [[Amphipod]]
File:Krill666.jpg| [[Krill]] 
File:Glaucus atlanticus 1 cropped.jpg| [[Glaucus atlanticus|Blue ocean slug]]
</gallery>
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====Holoplankton and meroplankton====
====Ichthyoplankton====
[[Ichthyoplankton]] are the [[Fish eggs|eggs]] and [[larvae]] of fish ("ichthyo" comes from the Greek word for ''fish''). They are planktonic because they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into [[juvenile fish]]. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.<ref name="NOAA">{{Cite web |date=2007-09-03 |title=What are Ichthyoplankton? |url=https://swfsc.noaa.gov/textblock.aspx?Division=FRD&id=6210 |url-status=dead |archive-url=https://web.archive.org/web/20180218090243/https://swfsc.noaa.gov/textblock.aspx?Division=FRD&id=6210 |archive-date=2018-02-18 |access-date=2011-07-22 |website=Southwest Fisheries Science Center}}</ref><ref name=Moser2006>{{Cite book|url=https://books.google.com/books?id=Qdzg0Vfql2sC&pg=PA269|title = The Ecology of Marine Fishes: California and Adjacent Waters|pages = 269–319|isbn = 9780520932470|last1 = Allen|first1 = Dr. Larry G.|last2 = Horn|first2 = Dr. Michael H.|date = 15 February 2006| publisher=University of California Press }}</ref>

<gallery mode="packed" heights="120px" style="float:left">
File:Squidu.jpg| Juvenile planktonic [[squid]]
File:Molalavdj.jpg| [[Ocean sunfish]] larvae (2.7mm)
File:FMIB 47039 Ostracion hoops.jpeg| [[Boxfish]] larva
</gallery>
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====Gelatinous zooplankton====
[[Gelatinous zooplankton]] include [[ctenophore]]s, [[Jellyfish|medusae]], [[salps]], and [[Chaetognatha]] in coastal waters. Jellyfish are slow swimmers, and most species form part of the plankton. Traditionally jellyfish have been viewed as [[Trophic level|trophic]] dead ends, minor players in the [[marine food web]], gelatinous organisms with a [[body plan]] largely based on water that offers little nutritional value or interest for other organisms apart from a few specialised predators such as the [[ocean sunfish]] and the [[leatherback sea turtle]].<ref name=Hamilton2016>Hamilton, G. (2016) [https://www.nature.com/news/polopoly_fs/1.19613!/menu/main/topColumns/topLeftColumn/pdf/531432a.pdf "The secret lives of jellyfish: long regarded as minor players in ocean ecology, jellyfish are actually important parts of the marine food web"]. ''Nature'', '''531'''(7595): 432–435. {{doi|10.1038/531432a}}</ref><ref name=Hays2018>[[Graeme Hays|Hays, G.C.]], Doyle, T.K. and Houghton, J.D. (2018) "A paradigm shift in the trophic importance of jellyfish?" ''Trends in ecology & evolution'', '''33'''(11): 874–884. {{doi|10.1016/j.tree.2018.09.001}}</ref> 

That view has recently been challenged. Jellyfish, and more gelatinous zooplankton in general, which include [[salp]]s and [[ctenophore]]s, are very diverse, fragile with no hard parts, difficult to see and monitor, subject to rapid population swings and often live inconveniently far from shore or deep in the ocean. It is difficult for scientists to detect and analyse jellyfish in the guts of predators, since they turn to mush when eaten and are rapidly digested.<ref name=Hamilton2016/> But jellyfish bloom in vast numbers, and it has been shown they form major components in the diets of [[tuna]], [[Tetrapturus|spearfish]] and [[swordfish]] as well as various birds and invertebrates such as [[octopus]], [[sea cucumber]]s, [[crab]]s and [[amphipod]]s.<ref>Cardona, L., De Quevedo, I.Á., Borrell, A. and Aguilar, A. (2012) "Massive consumption of gelatinous plankton by Mediterranean apex predators". ''PLOS ONE'', '''7'''(3): e31329. {{doi|10.1371/journal.pone.0031329}}</ref><ref name=Hays2018 /> "Despite their low energy density, the contribution of jellyfish to the energy budgets of predators may be much greater than assumed because of rapid digestion, low capture costs, availability, and selective feeding on the more energy-rich components. Feeding on jellyfish may make marine predators susceptible to ingestion of plastics."<ref name=Hays2018 /> According to a 2017 study, [[narcomedusae]] consume the greatest diversity of mesopelagic prey, followed by [[physonect]] [[siphonophore]]s, [[ctenophore]]s and [[cephalopod]]s.<ref name=Choy2017 /> 

<gallery mode="packed" heights="120px" style="float:left">
File:Parumbrosa polylobata 01.jpg| [[Jellyfish]]
File:Tunicate off Atauro island.jpg| This free-floating [[pyrosome]] is made up of hundreds of individual [[bioluminescent]] tunicates
File:23 salpchain frierson odfw (8253212250).jpg|[[Salp]] chain
</gallery>
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The importance of the so-called "jelly web" is only beginning to be understood, but it seems medusae, ctenophores and siphonophores can be key predators in deep pelagic food webs with ecological impacts similar to predator fish and squid. Traditionally gelatinous predators were thought ineffectual providers of marine trophic pathways, but they appear to have substantial and integral roles in deep [[pelagic food webs]].<ref name=Choy2017>Choy, C.A., Haddock, S.H. and Robison, B.H. (2017) "Deep pelagic food web structure as revealed by ''in situ'' feeding observations". ''Proceedings of the Royal Society B: Biological Sciences'', '''284'''(1868): 20172116. {{doi|10.1098/rspb.2017.2116}}. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>