Marine protists

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| quote = "Marine protists are a polyphyletic group of organisms playing major roles in the ecology and biogeochemistry of the oceans, including performing much of Earth's photosynthesis and driving the carbon, nitrogen, and silicon cycles. In addition, marine protists occupy key positions in the tree of life, including as the closest relatives of metazoans [animals]... Unicellular eukaryotes are often lumped as 'protists', a term that is useful despite its taxonomic irrelevance and origin as a definition by exclusion—a protist being any eukaryote that's not a plant, animal, or fungus".

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The ocean represents the largest continuous planetary ecosystem, hosting an enormous variety of organisms, which include microscopic biota such as unicellular eukaryotes (protists). Despite their small size, protists play key roles in marine biogeochemical cycles and harbour tremendous evolutionary diversity.{{cite journal |doi = 10.1126/science.1257594|title = Rethinking the marine carbon cycle: Factoring in the multifarious lifestyles of microbes|year = 2015|last1 = Worden|first1 = A. Z.|last2 = Follows|first2 = M. J.|last3 = Giovannoni|first3 = S. J.|last4 = Wilken|first4 = S.|last5 = Zimmerman|first5 = A. E.|last6 = Keeling|first6 = P. J.|journal = Science|volume = 347|issue = 6223|pmid = 25678667|s2cid = 206560125|doi-access = free}}{{cite journal |doi = 10.1126/science.1261605|title = Eukaryotic plankton diversity in the sunlit ocean|year = 2015|last1 = De Vargas|first1 = C.|last2 = Audic|first2 = S.|last3 = Henry|first3 = N.|last4 = Decelle|first4 = J.|last5 = Mahe|first5 = F.|last6 = Logares|first6 = R.|last7 = Lara|first7 = E.|last8 = Berney|first8 = C.|last9 = Le Bescot|first9 = N.|last10 = Probert|first10 = I.|last11 = Carmichael|first11 = M.|last12 = Poulain|first12 = J.|last13 = Romac|first13 = S.|last14 = Colin|first14 = S.|last15 = Aury|first15 = J.-M.|last16 = Bittner|first16 = L.|last17 = Chaffron|first17 = S.|last18 = Dunthorn|first18 = M.|last19 = Engelen|first19 = S.|last20 = Flegontova|first20 = O.|last21 = Guidi|first21 = L.|last22 = Horak|first22 = A.|last23 = Jaillon|first23 = O.|last24 = Lima-Mendez|first24 = G.|last25 = Luke|first25 = J.|last26 = Malviya|first26 = S.|last27 = Morard|first27 = R.|last28 = Mulot|first28 = M.|last29 = Scalco|first29 = E.|last30 = Siano|first30 = R.|journal = Science|volume = 348|issue = 6237|pmid = 25999516|s2cid = 12853481|url = https://archimer.ifremer.fr/doc/00270/38135/|display-authors = 1|hdl = 10261/117736|hdl-access = free}} Notwithstanding their significance for understanding the evolution of life on Earth and their role in marine food webs, as well as driving biogeochemical cycles to maintain habitability, little is known about their cell biology including reproduction, metabolism and signaling.{{cite journal |doi = 10.1091/mbc.E18-11-0724|title = Swimming, gliding, and rolling toward the mainstream: Cell biology of marine protists|year = 2019|last1 = Collier|first1 = Jackie L.|last2 = Rest|first2 = Joshua S.|journal = Molecular Biology of the Cell|volume = 30|issue = 11|pages = 1245–1248|pmid = 31084566|pmc = 6724603}} Most of the biological knowledge available is based on comparison of proteins from cultured species to homologs in genetically tractable model taxa.{{cite journal |doi = 10.1038/nature11681|title = Algal genomes reveal evolutionary mosaicism and the fate of nucleomorphs|year = 2012|last1 = Curtis|first1 = Bruce A.|last2 = Tanifuji|first2 = Goro|last3 = Burki|first3 = Fabien|last4 = Gruber|first4 = Ansgar|last5 = Irimia|first5 = Manuel|last6 = Maruyama|first6 = Shinichiro|last7 = Arias|first7 = Maria C.|last8 = Ball|first8 = Steven G.|last9 = Gile|first9 = Gillian H.|last10 = Hirakawa|first10 = Yoshihisa|last11 = Hopkins|first11 = Julia F.|last12 = Kuo|first12 = Alan|last13 = Rensing|first13 = Stefan A.|last14 = Schmutz|first14 = Jeremy|last15 = Symeonidi|first15 = Aikaterini|last16 = Elias|first16 = Marek|last17 = Eveleigh|first17 = Robert J. M.|last18 = Herman|first18 = Emily K.|last19 = Klute|first19 = Mary J.|last20 = Nakayama|first20 = Takuro|last21 = Oborník|first21 = Miroslav|last22 = Reyes-Prieto|first22 = Adrian|last23 = Armbrust|first23 = E. Virginia|last24 = Aves|first24 = Stephen J.|last25 = Beiko|first25 = Robert G.|last26 = Coutinho|first26 = Pedro|last27 = Dacks|first27 = Joel B.|last28 = Durnford|first28 = Dion G.|last29 = Fast|first29 = Naomi M.|last30 = Green|first30 = Beverley R.|journal = Nature|volume = 492|issue = 7427|pages = 59–65|pmid = 23201678|bibcode = 2012Natur.492...59C|s2cid = 4380094|display-authors = 1|doi-access = free}}{{cite journal |doi = 10.1126/science.1101156|title = The Genome of the Diatom Thalassiosira Pseudonana: Ecology, Evolution, and Metabolism|year = 2004|last1 = Armbrust|first1 = E. V.|last2 = Berges|first2 = John A.|last3 = Bowler|first3 = Chris|last4 = Green|first4 = Beverley R.|last5 = Martinez|first5 = Diego|last6 = Putnam|first6 = Nicholas H.|last7 = Zhou|first7 = Shiguo|last8 = Allen|first8 = Andrew E.|last9 = Apt|first9 = Kirk E.|last10 = Bechner|first10 = Michael|last11 = Brzezinski|first11 = Mark A.|last12 = Chaal|first12 = Balbir K.|last13 = Chiovitti|first13 = Anthony|last14 = Davis|first14 = Aubrey K.|last15 = Demarest|first15 = Mark S.|last16 = Detter|first16 = J. Chris|last17 = Glavina|first17 = Tijana|last18 = Goodstein|first18 = David|last19 = Hadi|first19 = Masood Z.|last20 = Hellsten|first20 = Uffe|last21 = Hildebrand|first21 = Mark|last22 = Jenkins|first22 = Bethany D.|last23 = Jurka|first23 = Jerzy|last24 = Kapitonov|first24 = Vladimir V.|last25 = Kröger|first25 = Nils|last26 = Lau|first26 = Winnie W. Y.|last27 = Lane|first27 = Todd W.|last28 = Larimer|first28 = Frank W.|last29 = Lippmeier|first29 = J. Casey|last30 = Lucas|first30 = Susan|display-authors = 1|journal = Science|volume = 306|issue = 5693|pages = 79–86|pmid = 15459382|bibcode = 2004Sci...306...79A|s2cid = 8593895|url = https://digital.library.unt.edu/ark:/67531/metadc885054/|url-access = subscription}}{{cite journal |doi = 10.1038/nature12221|title = Pan genome of the phytoplankton Emiliania underpins its global distribution|year = 2013|last1 = Read|first1 = Betsy A.|last2 = Kegel|first2 = Jessica|last3 = Klute|first3 = Mary J.|last4 = Kuo|first4 = Alan|last5 = Lefebvre|first5 = Stephane C.|last6 = Maumus|first6 = Florian|last7 = Mayer|first7 = Christoph|last8 = Miller|first8 = John|last9 = Monier|first9 = Adam|last10 = Salamov|first10 = Asaf|last11 = Young|first11 = Jeremy|last12 = Aguilar|first12 = Maria|last13 = Claverie|first13 = Jean-Michel|last14 = Frickenhaus|first14 = Stephan|last15 = Gonzalez|first15 = Karina|last16 = Herman|first16 = Emily K.|last17 = Lin|first17 = Yao-Cheng|last18 = Napier|first18 = Johnathan|last19 = Ogata|first19 = Hiroyuki|last20 = Sarno|first20 = Analissa F.|last21 = Shmutz|first21 = Jeremy|last22 = Schroeder|first22 = Declan|last23 = De Vargas|first23 = Colomban|last24 = Verret|first24 = Frederic|last25 = von Dassow|first25 = Peter|last26 = Valentin|first26 = Klaus|last27 = Van De Peer|first27 = Yves|last28 = Wheeler|first28 = Glen|last29 = Dacks|first29 = Joel B.|last30 = Delwiche|first30 = Charles F.|journal = Nature|volume = 499|issue = 7457|pages = 209–213|pmid = 23760476|bibcode = 2013Natur.499..209.|s2cid = 4428297|display-authors = 1|doi-access = free|hdl = 1854/LU-4120924|hdl-access = free}}{{cite journal |doi = 10.1371/journal.pbio.1001889|title = The Marine Microbial Eukaryote Transcriptome Sequencing Project (MMETSP): Illuminating the Functional Diversity of Eukaryotic Life in the Oceans through Transcriptome Sequencing|year = 2014|last1 = Keeling|first1 = Patrick J.|last2 = Burki|first2 = Fabien|last3 = Wilcox|first3 = Heather M.|last4 = Allam|first4 = Bassem|last5 = Allen|first5 = Eric E.|last6 = Amaral-Zettler|first6 = Linda A.|last7 = Armbrust|first7 = E. Virginia|last8 = Archibald|first8 = John M.|last9 = Bharti|first9 = Arvind K.|last10 = Bell|first10 = Callum J.|last11 = Beszteri|first11 = Bank|last12 = Bidle|first12 = Kay D.|last13 = Cameron|first13 = Connor T.|last14 = Campbell|first14 = Lisa|last15 = Caron|first15 = David A.|last16 = Cattolico|first16 = Rose Ann|last17 = Collier|first17 = Jackie L.|last18 = Coyne|first18 = Kathryn|last19 = Davy|first19 = Simon K.|last20 = Deschamps|first20 = Phillipe|last21 = Dyhrman|first21 = Sonya T.|last22 = Edvardsen|first22 = Bente|last23 = Gates|first23 = Ruth D.|last24 = Gobler|first24 = Christopher J.|last25 = Greenwood|first25 = Spencer J.|last26 = Guida|first26 = Stephanie M.|last27 = Jacobi|first27 = Jennifer L.|last28 = Jakobsen|first28 = Kjetill S.|last29 = James|first29 = Erick R.|last30 = Jenkins|first30 = Bethany|journal = PLOS Biology|volume = 12|issue = 6|pages = e1001889|pmid = 24959919|pmc = 4068987|display-authors = 1 | doi-access=free }} A main impediment to understanding the cell biology of these diverse eukaryotes is that protocols for genetic modification are available for only a small number of species{{hsp}}{{cite journal |doi = 10.1038/srep24951|title = A CRISPR/Cas9 system adapted for gene editing in marine algae|year = 2016|last1 = Nymark|first1 = Marianne|last2 = Sharma|first2 = Amit Kumar|last3 = Sparstad|first3 = Torfinn|last4 = Bones|first4 = Atle M.|last5 = Winge|first5 = Per|journal = Scientific Reports|volume = 6|page = 24951|pmid = 27108533|pmc = 4842962|bibcode = 2016NatSR...624951N}}{{cite journal |doi = 10.1186/s13007-016-0148-0|title = Editing of the urease gene by CRISPR-Cas in the diatom Thalassiosira pseudonana|year = 2016|last1 = Hopes|first1 = Amanda|last2 = Nekrasov|first2 = Vladimir|last3 = Kamoun|first3 = Sophien|last4 = Mock|first4 = Thomas|journal = Plant Methods|volume = 12|page = 49|pmid = 27904648|pmc = 5121945 | doi-access=free }} that represent neither the most ecologically relevant protists nor the breadth of eukaryotic diversity. Even so, in the decade to 2020, genome{{hsp}} and transcriptome sequencing initiatives{{hsp}} have resulted in nearly 120 million unigenes being identified in protists,{{cite journal |doi = 10.1038/s41467-017-02342-1|title = A global ocean atlas of eukaryotic genes|year = 2018|last1 = Carradec|first1 = Quentin|last2 = Pelletier|first2 = Eric|last3 = Da Silva|first3 = Corinne|last4 = Alberti|first4 = Adriana|last5 = Seeleuthner|first5 = Yoann|last6 = Blanc-Mathieu|first6 = Romain|last7 = Lima-Mendez|first7 = Gipsi|last8 = Rocha|first8 = Fabio|last9 = Tirichine|first9 = Leila|last10 = Labadie|first10 = Karine|last11 = Kirilovsky|first11 = Amos|last12 = Bertrand|first12 = Alexis|last13 = Engelen|first13 = Stefan|last14 = Madoui|first14 = Mohammed-Amin|last15 = Méheust|first15 = Raphaël|last16 = Poulain|first16 = Julie|last17 = Romac|first17 = Sarah|last18 = Richter|first18 = Daniel J.|last19 = Yoshikawa|first19 = Genki|last20 = Dimier|first20 = Céline|last21 = Kandels-Lewis|first21 = Stefanie|last22 = Picheral|first22 = Marc|last23 = Searson|first23 = Sarah|last24 = Jaillon|first24 = Olivier|last25 = Aury|first25 = Jean-Marc|last26 = Karsenti|first26 = Eric|last27 = Sullivan|first27 = Matthew B.|last28 = Sunagawa|first28 = Shinichi|last29 = Bork|first29 = Peer|last30 = Not|first30 = Fabrice|journal = Nature Communications|volume = 9|issue = 1|page = 373|pmid = 29371626|pmc = 5785536|bibcode = 2018NatCo...9..373C|display-authors = 1}} which is facilitating the development of genetic tools for model species.

File:Tree of Living Organisms 2.png

File:Phylogenetic relationships of marine protists 2.png with effigies of main marine protist representatives{{hsp}}{{cite journal |doi = 10.1038/s41592-020-0796-x|title = Genetic tool development in marine protists: Emerging model organisms for experimental cell biology|year = 2020|last1 = Faktorová|first1 = Drahomíra|last2 = Nisbet|first2 = R. Ellen R.|last3 = Fernández Robledo|first3 = José A.|last4 = Casacuberta|first4 = Elena|last5 = Sudek|first5 = Lisa|last6 = Allen|first6 = Andrew E.|last7 = Ares|first7 = Manuel|last8 = Aresté|first8 = Cristina|last9 = Balestreri|first9 = Cecilia|last10 = Barbrook|first10 = Adrian C.|last11 = Beardslee|first11 = Patrick|last12 = Bender|first12 = Sara|last13 = Booth|first13 = David S.|last14 = Bouget|first14 = François-Yves|last15 = Bowler|first15 = Chris|last16 = Breglia|first16 = Susana A.|last17 = Brownlee|first17 = Colin|last18 = Burger|first18 = Gertraud|last19 = Cerutti|first19 = Heriberto|last20 = Cesaroni|first20 = Rachele|last21 = Chiurillo|first21 = Miguel A.|last22 = Clemente|first22 = Thomas|last23 = Coles|first23 = Duncan B.|last24 = Collier|first24 = Jackie L.|last25 = Cooney|first25 = Elizabeth C.|last26 = Coyne|first26 = Kathryn|last27 = Docampo|first27 = Roberto|last28 = Dupont|first28 = Christopher L.|last29 = Edgcomb|first29 = Virginia|last30 = Einarsson|first30 = Elin|journal = Nature Methods|volume = 17|issue = 5|pages = 481–494|pmid = 32251396|pmc = 7200600|display-authors = 1}} 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].}}]]

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Protists can be divided broadly into four groups depending on whether their nutrition is plant-like, animal-like, fungal-like,{{cite journal | last1 = Whittaker | first1 = R.H. | last2 = Margulis | first2 = L. | year = 1978 | title = Protist classification and the kingdoms of organisms | journal = Biosystems | volume = 10 | issue = 1–2| pages = 3–18 | doi = 10.1016/0303-2647(78)90023-0 | pmid = 418827 | bibcode = 1978BiSys..10....3W }} or a mixture of these.{{cite journal | last1 = Faure | first1 = E | last2 = Not | first2 = F | last3 = Benoiston | first3 = AS | last4 = Labadie | first4 = K | last5 = Bittner | first5 = L | last6 = Ayata | first6 = SD | year = 2019 | title = Mixotrophic protists display contrasted biogeographies in the global ocean | journal = ISME Journal | volume = 13 | issue = 4| pages = 1072–1083 | doi = 10.1038/s41396-018-0340-5 | pmid = 30643201 | pmc = 6461780 | bibcode = 2019ISMEJ..13.1072F }}

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| footer = Choanoflagellates, unicellular "collared" flagellate protists, are thought to be the closest living relatives of the animals.{{cite journal |doi=10.1111/brv.12239 |pmid=26588818 |title=The origin of the animals and a 'Savannah' hypothesis for early bilaterian evolution |journal=Biological Reviews |volume=92 |issue=1 |pages=446–473 |year=2017 |last1=Budd |first1=Graham E |last2=Jensen |first2=Sören|doi-access=free }}

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File:Diatoms through the microscope.jpg|Diatoms are a major algae group generating about 20% of world oxygen production.[https://www.livescience.com/46250-teasing-apart-the-diatom-genome.html The Air You're Breathing? A Diatom Made That]

File:Triceratium morlandii var. morlandii.jpg|Fossil diatom frustule from 32 to 40 mya

File:Podocyrtis papalis Ehrenberg - Radiolarian (30448963206).jpg|Radiolarian

File:Gephyrocapsa oceanica color (lightened).jpg|Single-celled alga, Gephyrocapsa oceanica

File:CSIRO ScienceImage 7609 SEM dinoflagellate.jpg|Two dinoflagellates

File:Paramecium bursaria.jpg|A single-celled ciliate with green zoochlorellae living inside endosymbiotically

File:Euglenoid movement.jpg|Euglenoid

File:The ciliate Frontonia sp.jpg|This ciliate is digesting cyanobacteria. The cytostome or mouth is at the bottom right.

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| video1 = [https://www.youtube.com/watch?v=io731XY8fH8 How microscopic hunters get their lunch]

| video2 = [https://www.youtube.com/watch?v=OmoL8LlQwWQ Euglenoids: Single-celled shapeshifters]

| video3 = [https://www.youtube.com/watch?v=bPwVOggUp4M How do protozoans get around?]

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File:Frontonia ingesting a diatom.ogg|Ciliate ingesting a diatom

File:Amoeba engulfing diatom.ogv|Amoeba engulfing a diatom

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The fungus-like protist saprobes are specialized to absorb nutrients from nonliving organic matter, such as dead organisms or their wastes. For instance, many types of oomycetes grow on dead animals or algae. Marine saprobic protists have the essential function of returning inorganic nutrients to the water. This process allows for new algal growth, which in turn generates sustenance for other organisms along the food chain. Indeed, without saprobe species, such as protists, fungi, and bacteria, life would cease to exist as all organic carbon became "tied up" in dead organisms.Clark M A, Douglas M and Choi J (2018) Biology 2e, [https://openstax.org/books/biology-2e/pages/23-4-ecology-of-protists 23.4 "Ecology of Protists"], OpenStax, Houston, Texas. 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].{{cite journal |title=The oomycete Lagenisma coscinodisci hijacks host alkaloid synthesis during infection of a marine diatom|year = 2019|doi = 10.1038/s41467-019-12908-w|last1 = Vallet|first1 = Marine|last2 = Baumeister|first2 = Tim U. H.|last3 = Kaftan|first3 = Filip|last4 = Grabe|first4 = Veit|last5 = Buaya|first5 = Anthony|last6 = Thines|first6 = Marco|last7 = Svatoš|first7 = Aleš|last8 = Pohnert|first8 = Georg|journal = Nature Communications|volume = 10|issue = 1|page = 4938|pmid = 31666506|pmc = 6821873|bibcode = 2019NatCo..10.4938V}}

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| caption1 = Acantharian radiolarian hosts Phaeocystis symbionts.

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| caption2 = White Phaeocystis algal foam washing up on a beach

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Mixotrophs have no single trophic mode. A mixotroph is an organism that can use a mix of different 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.[https://www.irishexaminer.com/lifestyle/outdoors/richard-collins/beware-the-mixotrophs--they-can-destroy-entire-ecosystems-in-a-matter-of-hours-430358.html Beware the mixotrophs - they can destroy entire ecosystems 'in a matter of hours'] There are two types of eukaryotic mixotrophs: those with their own chloroplasts, and those with endosymbionts—and others that acquire them through kleptoplasty or by enslaving the entire phototrophic cell.[https://phys.org/news/2017-08-microscopic-body-snatchers-infest-oceans.html Microscopic body snatchers infest our oceans - Phys.org]

The distinction between plants and animals often breaks down in very small organisms. Possible combinations are photo- and chemotrophy, litho- and organotrophy, auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic.{{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 }} They can take advantage of different environmental conditions.{{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 }}

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 was mixotrophic.

Phaeocystis is an important algal genus found as part of the marine phytoplankton around the world. It has a polymorphic life cycle, ranging from free-living cells to large colonies.{{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}} 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 blooms.{{cite web |url= http://www.phaeocystis.org/|title = Welcome to the Phaeocystis antarctica genome sequencing project homepage }} As a result, Phaeocystis is an important contributor to the marine carbon{{cite journal |title=Rapid and early export of Phaeocystis antarctica blooms in the Ross Sea, Antarctica |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}} and sulfur cycles.{{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}} Phaeocystis species are endosymbionts to acantharian radiolarians.{{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}}{{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}}

File:Tintinnid ciliate Favella.jpg|Tintinnid ciliate Favella

File:Euglena mutabilis - 400x - 1 (10388739803) (cropped).jpg|Euglena mutabilis, a photosynthetic flagellate

File:Stichotricha secunda - 400x (14974779356).jpg|Zoochlorellae (green) living inside the ciliate Stichotricha secunda

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{{main|Protist locomotion}}

Another way of categorising protists is according to their mode of locomotion. Many unicellular protists, particularly protozoans, are motile and can generate movement using flagella, cilia or pseudopods. Cells which use flagella for movement are usually referred to as flagellates, cells which use cilia are usually referred to as ciliates, and cells which use pseudopods are usually referred to as amoeba or amoeboids. Other protists are not motile, and consequently have no movement mechanism.

File:Flagellum-beating.svg

Flagella are used in prokaryotes (archaea and bacteria) as well as protists. In addition, both flagella and cilia are widely used in eukaryotic cells (plant and animal) apart from protists.

The regular beat patterns of eukaryotic cilia and flagella generates motion on a cellular level. Examples range from the propulsion of single cells such as the swimming of spermatozoa to the transport of fluid along a stationary layer of cells such as in a respiratory tract. Though eukaryotic flagella and motile cilia are ultrastructurally identical, the beating pattern of the two organelles can be different. In the case of flagella, the motion is often planar and wave-like, whereas the motile cilia often perform a more complicated three-dimensional motion with a power and recovery stroke.

Eukaryotic flagella—those of animal, plant, and protist cells—are complex cellular projections that lash back and forth. Eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia[http://www.encyclopedia.com/doc/1O6-undulipodium.html A Dictionary of Biology], 2004, accessed 2011-01-01. to emphasize their distinctive wavy appendage role in cellular function or motility. Primary cilia are immotile, and are not undulipodia.

File:Marine flagellates.jpg, Abollifer, Bodo, Rhynchomonas, Kiitoksia, Allas, and Metromonas{{hsp}}Patterson, David J. (2000) [http://tolweb.org/accessory/flagellates?acc_id=50 "Flagellates: Heterotrophic Protists With Flagella"] Tree of Life.}}]]

File:Cillia1.png

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Ciliates generally have hundreds to thousands of cilia that are densely packed together in arrays. Like the flagella, the cilia are powered by specialised molecular motors. An efficient forward stroke is made with a stiffened flagellum, followed by an inefficient backward stroke made with a relaxed flagellum. During movement, an individual cilium deforms as it uses the high-friction power strokes and the low-friction recovery strokes. Since there are multiple cilia packed together on an individual organism, they display collective behaviour in a metachronal rhythm. This means the deformation of one cilium is in phase with the deformation of its neighbor, causing deformation waves that propagate along the surface of the organism. These propagating waves of cilia are what allow the organism to use the cilia in a coordinated manner to move. A typical example of a ciliated microorganism is the Paramecium, a one-celled, ciliated protozoan covered by thousands of cilia. The cilia beating together allow the Paramecium to propel through the water at speeds of 500 micrometers per second.{{cite journal|last=Lauga|first=Eric|author2=Thomas R Powers|title=The hydrodynamics of swimming microorganisms|journal=Reports on Progress in Physics|date=25 August 2009|volume=72|issue=9|pages=096601|doi=10.1088/0034-4885/72/9/096601|bibcode=2009RPPh...72i6601L|arxiv=0812.2887|s2cid=3932471}}

File:Chlamydomonas (10000x).jpg|Green algal flagellate (Chlamydomonas)

File:Инфузория туфелька поедает бактерии!.gif|Paramecium feeding on bacteria

File:Oxytricha trifallax.jpg|The ciliate Oxytricha trifallax with cilia clearly visible

File:Collection Penard MHNG Specimen 05bis-1-1 Amoeba proteus.tif|Amoeba with ingested diatoms

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{{plankton sidebar|taxonomy}}

Algae is an informal term for a widespread and diverse group of photosynthetic protists which are not necessarily closely related and are thus polyphyletic. Marine algae can be divided into six groups: green, red and brown algae, euglenophytes, dinoflagellates and diatoms.

Dinoflagellates and diatoms are important components of marine algae and have their own sections below. Euglenophytes are a phylum of unicellular flagellates with only a few marine members.

Not all algae are microscopic. Green, red and brown algae all have multicellular macroscopic forms that make up the familiar seaweeds. Green algae, an informal group, contains about 8,000 recognised species.{{cite journal | vauthors = Guiry MD | title = How many species of algae are there? | journal = Journal of Phycology | volume = 48 | issue = 5 | pages = 1057–63 | date = October 2012 | pmid = 27011267 | doi = 10.1111/j.1529-8817.2012.01222.x| bibcode = 2012JPcgy..48.1057G | s2cid = 30911529 }} Many species live most of their lives as single cells or are filamentous, while others form colonies made up from long chains of cells, or are highly differentiated macroscopic seaweeds. Red algae, a (disputed) phylum contains about 7,000 recognised species,{{Cite web|url=http://www.algaebase.org/browse/taxonomy/?id=97240|title=Algaebase|last1=Guiry|first1=M.D.|last2=Guiry|first2=G.M.|date=2016|website=www.algaebase.org|access-date=November 20, 2016}} mostly multicellular and including many notable seaweeds.{{cite book|title=Seaweeds|publisher=Life Series. Natural History Museum, London|year=2002|isbn=978-0-565-09175-0|author=D. Thomas}} Brown algae form a class containing about 2,000 recognised species,{{Cite book|url=https://books.google.com/books?id=s1P855ZWc0kC&pg=166|title=Algae : an introduction to phycology|last1=Hoek|first1=Christiaan|last2=den Hoeck|first2=Hoeck Van|last3=Mann|first3=David|last4=Jahns|first4=H.M.|date=1995|publisher=Cambridge University Press|isbn=9780521316873|oclc=443576944|page=166}} mostly multicellular and including many seaweeds such as kelp.

Unlike higher plants, algae lack roots, stems, or leaves. They can be classified by size as microalgae or macroalgae.

Microalgae are the microscopic types of algae, not visible to the naked eye. They are mostly unicellular species which exist as individuals or in chains or groups, though some are multicellular. Microalgae are important components of the marine protists discussed above, as well as the phytoplankton discussed below. They are very diverse. It has been estimated there are 200,000–800,000 species of which about 50,000 species have been described.Starckx, Senne (31 October 2012) [http://www.flanderstoday.eu/current-affairs/place-sun A place in the sun - Algae is the crop of the future, according to researchers in Geel] {{Webarchive|url=https://web.archive.org/web/20171107004501/http://www.flanderstoday.eu/current-affairs/place-sun |date=7 November 2017 }} Flanders Today, Retrieved 8 December 2012 Depending on the species, their sizes range from a few micrometers (μm) to a few hundred micrometers. They are specially adapted to an environment dominated by viscous forces.

File:Chlamydomonas globosa - 400x (13263097835).jpg|Chlamydomonas globosa, a unicellular green alga with two flagella just visible at bottom left

File:Инфузории Ophridium versatile.jpg|Chlorella vulgaris, a common green microalgae, in endosymbiosis with a ciliate{{cite journal|last1 = Duval|first1 = B.|last2 = Margulis|first2 = L.|year = 1995|title = The microbial community of Ophrydium versatile colonies: endosymbionts, residents, and tenants|journal = Symbiosis|volume = 18|pages = 181–210|pmid = 11539474 }}

File:Centric diatom.jpg|Centric diatom

File:Dinoflagellates.jpg|Dinoflagellates

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Macroalgae are the larger, multicellular and more visible types of algae, commonly called seaweeds. Seaweeds usually grow in shallow coastal waters where they are anchored to the seafloor by a holdfast. Like microalgae, macroalgae (seaweeds) can be regarded as marine protists since they are not true plants. But they are not microorganisms, so they are not within the scope of this article.

Unicellular organisms are usually microscopic, less than one tenth of a millimeter long. There are exceptions. Mermaid's wineglass, a genus of subtropical green algae, is single-celled but remarkably large and complex in form with a single large nucleus, making it a model organism for studying cell biology.{{cite journal|last=Mandoli|first=DF|year=1998|title=Elaboration of Body Plan and Phase Change during Development of Acetabularia: How Is the Complex Architecture of a Giant Unicell Built?|journal=Annual Review of Plant Physiology and Plant Molecular Biology|volume=49|pages=173–198|pmid=15012232|doi=10.1146/annurev.arplant.49.1.173|s2cid=6241264}} Another single-celled algae, Caulerpa taxifolia, has the appearance of a vascular plant including "leaves" arranged neatly up stalks like a fern. Selective breeding in aquariums to produce hardier strains resulted in an accidental release into the Mediterranean where it has become an invasive species known colloquially as killer algae.{{cite journal | author1 = Pierre Madl | author2 = Maricela Yip | title = Literature Review of Caulerpa taxifolia | journal = BUFUS-Info | volume = 19 | issue = 31 | year = 2004 | url = http://biophysics.sbg.ac.at/ct/caulerpa.htm | access-date = 12 May 2020 | archive-date = 8 October 2022 | archive-url = https://web.archive.org/web/20221008200554/http://biophysics.sbg.ac.at/ct/caulerpa.htm | url-status = dead }}

File:Diatom3.jpg

Diatoms are photosynthetic unicellular algae populating the oceans and other waters around the globe. They form a (disputed) phylum containing about 100,000 recognised species. Diatoms generate about 20 per cent of all oxygen produced on the planet each year, and take in over 6.7 billion metric tons of silicon each year from the waters in which they live.{{cite journal | last1 = Treguer | first1 = P. | last2 = Nelson | first2 = D. M. | last3 = Van Bennekom | first3 = A. J. | last4 = Demaster | first4 = D. J. | last5 = Leynaert | first5 = A. | last6 = Queguiner | first6 = B. | year = 1995 | title = The Silica Balance in the World Ocean: A Reestimate | journal = Science | volume = 268 | issue = 5209| pages = 375–9 | pmid = 17746543 | doi = 10.1126/science.268.5209.375 | bibcode = 1995Sci...268..375T | s2cid = 5672525 }} They produce 25–45% of the total primary production of organic material in the oceans,{{cite journal |doi = 10.1029/95GB01070|title = Production and dissolution of biogenic silica in the ocean: Revised global estimates, comparison with regional data and relationship to biogenic sedimentation|year = 1995|last1 = Nelson|first1 = David M.|last2 = Tréguer|first2 = Paul|last3 = Brzezinski|first3 = Mark A.|last4 = Leynaert|first4 = Aude|last5 = Quéguiner|first5 = Bernard|journal = Global Biogeochemical Cycles|volume = 9|issue = 3|pages = 359–372|bibcode = 1995GBioC...9..359N}}{{cite journal |doi = 10.1073/pnas.1509523113|title = Insights into global diatom distribution and diversity in the world's ocean|year = 2016|last1 = Malviya|first1 = Shruti|last2 = Scalco|first2 = Eleonora|last3 = Audic|first3 = Stéphane|last4 = Vincent|first4 = Flora|last5 = Veluchamy|first5 = Alaguraj|last6 = Poulain|first6 = Julie|last7 = Wincker|first7 = Patrick|last8 = Iudicone|first8 = Daniele|last9 = De Vargas|first9 = Colomban|last10 = Bittner|first10 = Lucie|last11 = Zingone|first11 = Adriana|last12 = Bowler|first12 = Chris|journal = Proceedings of the National Academy of Sciences|volume = 113|issue = 11|pages = E1516–E1525|pmid = 26929361|pmc = 4801293|bibcode = 2016PNAS..113E1516M|s2cid = 22035749|doi-access = free}}{{cite journal |doi = 10.1038/s41561-017-0028-x|title = Influence of diatom diversity on the ocean biological carbon pump|year = 2018|last1 = Tréguer|first1 = Paul|last2 = Bowler|first2 = Chris|last3 = Moriceau|first3 = Brivaela|last4 = Dutkiewicz|first4 = Stephanie|last5 = Gehlen|first5 = Marion|last6 = Aumont|first6 = Olivier|last7 = Bittner|first7 = Lucie|last8 = Dugdale|first8 = Richard|last9 = Finkel|first9 = Zoe|last10 = Iudicone|first10 = Daniele|last11 = Jahn|first11 = Oliver|last12 = Guidi|first12 = Lionel|last13 = Lasbleiz|first13 = Marine|last14 = Leblanc|first14 = Karine|last15 = Levy|first15 = Marina|last16 = Pondaven|first16 = Philippe|journal = Nature Geoscience|volume = 11|issue = 1|pages = 27–37|bibcode = 2018NatGe..11...27T|s2cid = 134885922| url=https://hal.science/hal-01667978/file/treguer2017.pdf }} owing to their prevalence in open-ocean regions when total phytoplankton biomass is maximal.{{cite journal |doi = 10.1126/science.1218740|title = Eddy-Driven Stratification Initiates North Atlantic Spring Phytoplankton Blooms|year = 2012|last1 = Mahadevan|first1 = Amala|last2 = d'Asaro|first2 = Eric|last3 = Lee|first3 = Craig|last4 = Perry|first4 = Mary Jane|journal = Science|volume = 337|issue = 6090|pages = 54–58|pmid = 22767922|bibcode = 2012Sci...337...54M|s2cid = 42312402}}{{cite journal |doi = 10.1038/s41579-019-0222-5|title = Scientists' warning to humanity: Microorganisms and climate change|year = 2019|last1 = Cavicchioli|first1 = Ricardo|last2 = Ripple|first2 = William J.|last3 = Timmis|first3 = Kenneth N.|last4 = Azam|first4 = Farooq|last5 = Bakken|first5 = Lars R.|last6 = Baylis|first6 = Matthew|last7 = Behrenfeld|first7 = Michael J.|last8 = Boetius|first8 = Antje|last9 = Boyd|first9 = Philip W.|last10 = Classen|first10 = Aimée T.|last11 = Crowther|first11 = Thomas W.|last12 = Danovaro|first12 = Roberto|last13 = Foreman|first13 = Christine M.|last14 = Huisman|first14 = Jef|last15 = Hutchins|first15 = David A.|last16 = Jansson|first16 = Janet K.|last17 = Karl|first17 = David M.|last18 = Koskella|first18 = Britt|last19 = Mark Welch|first19 = David B.|last20 = Martiny|first20 = Jennifer B. H.|last21 = Moran|first21 = Mary Ann|last22 = Orphan|first22 = Victoria J.|last23 = Reay|first23 = David S.|last24 = Remais|first24 = Justin V.|last25 = Rich|first25 = Virginia I.|last26 = Singh|first26 = Brajesh K.|last27 = Stein|first27 = Lisa Y.|last28 = Stewart|first28 = Frank J.|last29 = Sullivan|first29 = Matthew B.|last30 = Van Oppen|first30 = Madeleine J. H.|journal = Nature Reviews Microbiology|volume = 17|issue = 9|pages = 569–586|pmid = 31213707|pmc = 7136171|display-authors = 29}} 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

Diatoms are enclosed in protective silica (glass) shells called frustules. They are classified by the shape of these glass cages in which they live, and which they build as they grow. Each frustule is made from two interlocking parts covered with tiny holes through which the diatom exchanges nutrients and wastes.Wassilieff, Maggy (2006) [https://teara.govt.nz/en/plankton/page-1 "Plankton - Plant plankton"], Te Ara - the Encyclopedia of New Zealand. Accessed: 2 November 2019. Dead diatoms drift to the ocean floor where, over millions of years, the remains of their frustules can build up as much as half a mile deep.{{Cite web|url=https://www.kcl.ac.uk/sspp/departments/geography/people/academic/drake/Research/The-Sahara-Megalakes-Project/Lake-Megachad.aspx|title=King's College London - Lake Megachad|website=www.kcl.ac.uk|language=en-GB|access-date=2018-05-05}} Diatoms have relatively high sinking speeds compared with other phytoplankton groups, and they account for about 40% of particulate carbon exported to ocean depths.{{cite journal |doi = 10.1038/s41586-019-1098-2|title = Multi-faceted particle pumps drive carbon sequestration in the ocean|year = 2019|last1 = Boyd|first1 = Philip W.|last2 = Claustre|first2 = Hervé|last3 = Levy|first3 = Marina|last4 = Siegel|first4 = David A.|last5 = Weber|first5 = Thomas|journal = Nature|volume = 568|issue = 7752|pages = 327–335|pmid = 30996317|bibcode = 2019Natur.568..327B|s2cid = 119513489|url = https://hal.archives-ouvertes.fr/hal-02117441/file/pdf%20merged%20of%20final%20submission%20317960_6_merged_1547169923.pdf}}

File:Diatoms (248 05) Various diatoms.jpg|Diatoms are one of the most common types of phytoplankton.

File:Diatom Helipelta metil.jpg|Their protective shells (frustles) are made of silicon.

File:Diatom - Triceratium favus.jpg

File:Diatom - Isthmia nervosa - 400x (16237138292).jpg|

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Physically driven seasonal enrichments in surface nutrients favour diatom blooms. Anthropogenic climate change will directly affect these seasonal cycles, changing the timing of blooms and diminishing their biomass, which will reduce primary production and CO₂ uptake.{{cite journal |doi = 10.1002/gbc.20050|title = Annual cycles of ecological disturbance and recovery underlying the subarctic Atlantic spring plankton bloom|year = 2013|last1 = Behrenfeld|first1 = Michael J.|last2 = Doney|first2 = Scott C.|last3 = Lima|first3 = Ivan|last4 = Boss|first4 = Emmanuel S.|last5 = Siegel|first5 = David A.|journal = Global Biogeochemical Cycles|volume = 27|issue = 2|pages = 526–540|bibcode = 2013GBioC..27..526B|doi-access = free|hdl = 1912/6250|hdl-access = free}} Remote sensing data suggests there was a global decline of diatoms between 1998 and 2012, particularly in the North Pacific, associated with shallowing of the surface mixed layer and lower nutrient concentrations.{{cite journal |doi = 10.1002/2015GB005139|title = Recent decadal trends in global phytoplankton composition|year = 2015|last1 = Rousseaux|first1 = Cecile S.|last2 = Gregg|first2 = Watson W.|journal = Global Biogeochemical Cycles|volume = 29|issue = 10|pages = 1674–1688|bibcode = 2015GBioC..29.1674R|doi-access = free}}

File:Diatom algae Amphora sp.jpg|Silicified frustule of a pennate diatom with two overlapping halves

File:Fjouenne sbrmvr012w 20070924163039 small.jpg|Guinardia delicatula, a diatom responsible for diatom blooms in the North Sea{{hsp}}{{cite journal|last1 = Arsenieff|first1 = L.|last2 = Simon|first2 = N.|last3 = Rigaut-Jalabert|first3 = F.|last4 = Le Gall|first4 = F.|last5 = Chaffron|first5 = S.|last6 = Corre|first6 = E.|last7 = Com|first7 = E.|last8 = Bigeard|first8 = E.|last9 = Baudoux|first9 = A.C.|year = 2018|title = First Viruses Infecting the Marine Diatom Guinardia delicatula|journal = Frontiers in Microbiology|volume = 9|page = 3235|doi = 10.3389/fmicb.2018.03235|pmid = 30687251|pmc = 6334475|doi-access = free}}|alt=Guinardia delicatula, a diatom responsible for diatom blooms in the North Sea

File:Pinnularia major.jpg| There are over 100,000 species of diatoms accounting for 25–45% of the ocean's primary production

File:CSIRO ScienceImage 7233 diatom.jpg| Linked diatoms

File:Pennate diatom infected with two chytrid-like fungal pathogens.png| Pennate diatom from an Arctic meltpond, infected with two chytrid-like fungal pathogens. Scale bar = 10 μm.{{cite journal |doi = 10.1038/s42003-020-0891-7|title = Chytrid fungi distribution and co-occurrence with diatoms correlate with sea ice melt in the Arctic Ocean|year = 2020|last1 = Kilias|first1 = Estelle S.|last2 = Junges|first2 = Leandro|last3 = Šupraha|first3 = Luka|last4 = Leonard|first4 = Guy|last5 = Metfies|first5 = Katja|last6 = Richards|first6 = Thomas A.|journal = Communications Biology|volume = 3|issue = 1|page = 183|pmid = 32317738|pmc = 7174370|s2cid = 216033140}} 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

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Coccolithophores are minute unicellular photosynthetic protists with two flagella for locomotion. Most of them are protected by calcium carbonate shells covered with ornate circular plates or scales called coccoliths. The term coccolithophore derives from the Greek for a seed carrying stone, referring to their small size and the coccolith stones they carry. Under the right conditions they bloom, like other phytoplankton, and can turn the ocean milky white.Wassilieff, Maggy (2006) [https://teara.govt.nz/en/photograph/5130/a-coccolithophore "A coccolithophore"], Te Ara - the Encyclopedia of New Zealand. Accessed: 2 November 2019.

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File:Braarudosphaera bigelowii.jpg has an unusual shell with a regular dodecahedral structure about 10 micrometers across.Hagino, K., Onuma, R., Kawachi, M. and Horiguchi, T. (2013) "Discovery of an endosymbiotic nitrogen-fixing cyanobacterium UCYN-A in Braarudosphaera bigelowii (Prymnesiophyceae)". PLoS One, 8(12): e81749. {{doi|10.1371/journal.pone.0081749|doi-access=free}}.]]

File:Emiliania huxleyi.jpg|The coccolithophore Emiliania huxleyi

File:Cwall99 lg.jpg|Algae bloom of Emiliania huxleyi off the southern coast of England

File:JRYSEM-247-05-azurapl.jpg|{{center|Coccolithophores named after the BBC documentary series
The Blue Planet}}

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{{see also|Mixotrophic dinoflagellate|Predatory dinoflagellate}}

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Dinoflagellates are usually positioned as part of the algae group, and form a phylum of unicellular flagellates with about 2,000 marine species.{{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 }} The 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. Like other phytoplankton, dinoflagellates are r-strategists which under right conditions can bloom and create red tides. Excavates may be the most basal flagellate lineage.

By trophic orientation dinoflagellates are all over the place. Some dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy).{{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}} Some species are endosymbionts of marine animals and other protists, and play an important part in the biology of coral reefs. 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 Mesodinium rubrum, which sequester their chloroplasts from a specific cryptophyte clade (Geminigera/Plagioselmis/Teleaulax)".

File:Gyrodinium dinoflagellate.jpg|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.

File:Dinophysis acuta.jpg|The dinoflagellate Dinophysis acuta

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Dinoflagellates often live in symbiosis with other organisms. Many nassellarian radiolarians house dinoflagellate symbionts within their tests.{{Cite book|title=Handbook of the Protists|last1=Boltovskoy|first1=Demetrio|last2=Anderson|first2=O. Roger|last3=Correa|first3=Nancy M.|chapter=Radiolaria and Phaeodaria |date=2017|publisher=Springer, Cham|isbn=9783319281476|pages=731–763|language=en|doi=10.1007/978-3-319-28149-0_19}} 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.{{Cite book|title=Radiolaria|last=Anderson|first=O. R.|publisher=Springer Science & Business Media|year=1983}} There is evidence from DNA analysis that dinoflagellate symbiosis with radiolarians evolved independently from other dinoflagellate symbioses, such as with foraminifera.{{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=free}}

Some dinoflagellates are bioluminescent. At night, ocean water can light up internally and sparkle with blue light because of these dinoflagellates.{{cite book |last1=Castro |first1=Peter |first2=Michael E. |last2=Huber |title=Marine Biology |url=https://archive.org/details/marinebiology00cast_419 |url-access=limited |publisher=McGraw Hill |year=2010 |isbn=978-0071113021 |pages=[https://archive.org/details/marinebiology00cast_419/page/n110 95] |edition=8th | name-list-style = vanc}}{{cite journal | vauthors = Hastings JW | title = Chemistries and colors of bioluminescent reactions: a review | journal = Gene | volume = 173 | issue = 1 Spec No | pages = 5–11 | year = 1996 | pmid = 8707056 | doi = 10.1016/0378-1119(95)00676-1}} Bioluminescent dinoflagellates possess scintillons, individual cytoplasmic bodies which contain dinoflagellate luciferase, the main enzyme involved in the luminescence. The luminescence, sometimes called the phosphorescence of the sea, occurs as brief (0.1 sec) blue flashes or sparks when individual scintillons are stimulated, usually by mechanical disturbances from, for example, a boat or a swimmer or surf.{{cite journal | vauthors = Haddock SH, Moline MA, Case JF | title = Bioluminescence in the sea | journal = Annual Review of Marine Science | volume = 2 | pages = 443–93 | date = 2009 | pmid = 21141672 | doi = 10.1146/annurev-marine-120308-081028 | bibcode = 2010ARMS....2..443H| s2cid = 3872860 }}

File:Ceratium tripos.jpg|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.{{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}}

File:Karenia brevis.jpg|Karenia brevis produces red tides highly toxic to humans.{{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 }}

File:Algal bloom(akasio) by Noctiluca in Nagasaki.jpg|Red tide

File:Noctiluca scintillans unica.jpg|Noctiluca scintillans, a bioluminescent dinoflagellate{{cite journal|last1 = Buskey|first1 = E.J.|year = 1995|title = Growth and bioluminescence of Noctiluca scintillans on varying algal diets|journal = Journal of Plankton Research|volume = 17|issue = 1|pages = 29–40|doi = 10.1093/plankt/17.1.29 }}

File:Ornithocercus heteroporus (probably).jpg|Ornithocercus heteroporus - prominent lists on display

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Protozoans are protists which feed on organic matter such as other microorganisms or organic tissues and debris.{{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}}{{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}} 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.{{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}}{{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 }} 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 heterotrophy.

Marine protozoans include zooflagellates, foraminiferans, radiolarians and some dinoflagellates.

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Radiolarians are unicellular predatory protists encased in elaborate globular shells, typically between 0.1 and 0.2 millimetres in size, 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 microfossils, provide valuable information about past oceanic conditions.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.

File:Mikrofoto.de-Radiolarien 6.jpg|Like diatoms, radiolarians come in many shapes.

File:Theocotylissa ficus Ehrenberg - Radiolarian (34638920262).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

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closely replicate some radiolarian shell patterns.{{cite journal | last1 = Varea | first1 = C. | last2 = Aragon | first2 = J.L. | last3 = Barrio | first3 = R.A. | year = 1999 | title = Turing patterns on a sphere | journal = Physical Review E | volume = 60 | issue = 4| pages = 4588–92 | doi = 10.1103/PhysRevE.60.4588 | pmid = 11970318 | bibcode = 1999PhRvE..60.4588V }}

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File:Cladococcus abietinus.jpg|Cladococcus abietinus

File:Cleveiplegma boreale.jpg|Cleveiplegma boreale

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Like radiolarians, foraminiferans (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 tests, are chambered (forams add more chambers as they grow). The shells are usually made of calcite, but are sometimes made of agglutinated sediment particles or chiton, and (rarely) of silica. Most forams are benthic, but about 40 species are planktic.{{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}} They are widely researched with well established fossil records which allow scientists to infer a lot about past environments and climates.

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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:Nummulitids.jpg|Fossil nummulitid forams of various sizes from the Eocene

File:All Gizah Pyramids.jpg|The Egyptian pyramids were constructed from limestone that contained nummulites.[http://www.ucl.ac.uk/GeolSci/micropal/foram.html#histofstudy Foraminifera: History of Study], University College London. Retrieved: 18 November 2019.

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A number of forams are mixotrophic (see below). These have unicellular algae as endosymbionts, from diverse lineages such as the green algae, red algae, golden algae, diatoms, and dinoflagellates. Mixotrophic foraminifers are particularly common in nutrient-poor oceanic waters.[https://books.google.com/books?id=QvvlBwAAQBAJ&dq=%22The+symbiont-bearing+foraminifera+are+particularly+common+in+nutrient-poor+oceanic+waters%22&pg=PA22 Advances in Microbial Ecology, Volume 11] Some forams are kleptoplastic, retaining chloroplasts from ingested algae to conduct photosynthesis.{{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}}

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File:Amoeba proteus 2.jpg|Naked amoeba 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|Xenogenic testate amoeba covered in diatoms (from [https://commons.wikimedia.org/wiki/Commons:P%C3%A9nard_project Penard's Amoeba Collection])

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Marine ciliates are major grazers of the phytoplankton.{{cite journal |doi = 10.4319/lo.2004.49.1.0051|title = Phytoplankton growth, microzooplankton grazing, and carbon cycling in marine systems|year = 2004|last1 = Calbet|first1 = Albert|last2 = Landry|first2 = Michael R.|journal = Limnology and Oceanography|volume = 49|issue = 1|pages = 51–57|bibcode = 2004LimOc..49...51C|hdl = 10261/134985| s2cid=22995996 |hdl-access = free}}{{cite journal |doi = 10.3389/fmars.2018.00272|title = Phytoplankton Community Dynamic: A Driver for Ciliate Trophic Strategies|year = 2018|last1 = Haraguchi|first1 = Lumi|last2 = Jakobsen|first2 = Hans H.|last3 = Lundholm|first3 = Nina|last4 = Carstensen|first4 = Jacob|journal = Frontiers in Marine Science|volume = 5|s2cid = 51925344|doi-access = free}} 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

Phytoplankton primary production supports higher trophic levels and fuels microbial remineralization.{{cite journal |doi = 10.3354/meps010257|title = The Ecological Role of Water-Column Microbes in the Sea|year = 1983|last1 = Azam|first1 = F.|last2 = Fenchel|first2 = T.|last3 = Field|first3 = JG|last4 = Gray|first4 = JS|last5 = Meyer-Reil|first5 = LA|last6 = Thingstad|first6 = F.|journal = Marine Ecology Progress Series|volume = 10|pages = 257–263|bibcode = 1983MEPS...10..257A|doi-access = free}}{{cite journal |doi = 10.4319/lo.1988.33.5.1225|title = Role of microbes in pelagic food webs: A revised concept|year = 1988|last1 = Sherr|first1 = Evelyn|last2 = Sherr|first2 = Barry|journal = Limnology and Oceanography|volume = 33|issue = 5|pages = 1225–1227|bibcode = 1988LimOc..33.1225S|doi-access = free}} The dominant pelagic grazers of phytoplankton are typically associated with distinct operating modes of the food web compartments and nutrient cycling. Heterotrophic protist grazers and microzooplankton dominance is usually associated with the microbial loop and regenerated production; while mesozooplankton is associated with a linear food chain and export production.{{cite journal |doi = 10.1146/annurev.es.19.110188.000315|title = Marine Plankton Food Chains|year = 1988|last1 = Fenchel|first1 = T.|journal = Annual Review of Ecology and Systematics|volume = 19|pages = 19–38}}{{cite journal |doi = 10.1029/2005GB002511|title = Biogeochemical fluxes through mesozooplankton|year = 2006|last1 = Buitenhuis|first1 = Erik|last2 = Le Quéré|first2 = Corinne|last3 = Aumont|first3 = Olivier|last4 = Beaugrand|first4 = Grégory|last5 = Bunker|first5 = Adrian|last6 = Hirst|first6 = Andrew|last7 = Ikeda|first7 = Tsutomu|last8 = O'Brien|first8 = Todd|last9 = Piontkovski|first9 = Sergey|last10 = Straile|first10 = Dietmar|journal = Global Biogeochemical Cycles|volume = 20|issue = 2|pages = n/a|bibcode = 2006GBioC..20.2003B|doi-access = free|hdl = 2115/13694|hdl-access = free}} Grazing on particulate primary production in the global ocean surface is ~10–15% for mesozooplankton and 59–75% for microzooplankton,{{cite journal |doi = 10.4319/lo.1997.42.1.0001|title = Photosynthetic rates derived from satellite-based chlorophyll concentration|year = 1997|last1 = Behrenfeld|first1 = Michael J.|last2 = Falkowski|first2 = Paul G.|journal = Limnology and Oceanography|volume = 42|issue = 1|pages = 1–20|bibcode = 1997LimOc..42....1B| s2cid=15857675 |doi-access = free}}{{cite journal |doi = 10.4319/lo.2001.46.7.1824|title = Mesozooplankton grazing effect on primary production: A global comparative analysis in marine ecosystems|year = 2001|last1 = Calbet|first1 = Albert|journal = Limnology and Oceanography|volume = 46|issue = 7|pages = 1824–1830|bibcode = 2001LimOc..46.1824C|hdl = 10261/49263| s2cid=85461746 |hdl-access = free}}{{cite journal |doi = 10.1016/j.icesjms.2004.03.011|title = Microzooplankton production in the oceans|year = 2004|last1 = Landry|first1 = Michael R.|last2 = Calbet|first2 = Albert|journal = ICES Journal of Marine Science|volume = 61|issue = 4|pages = 501–507|doi-access = free| bibcode=2004ICJMS..61..501L }}{{cite journal |doi = 10.1029/2009GB003601|title = Biogeochemical fluxes through microzooplankton|year = 2010|last1 = Buitenhuis|first1 = Erik T.|last2 = Rivkin|first2 = Richard B.|last3 = Sailley|first3 = Sévrine|last4 = Le Quéré|first4 = Corinne|journal = Global Biogeochemical Cycles|volume = 24|issue = 4|pages = n/a|bibcode = 2010GBioC..24.4015B| s2cid=131413083 |doi-access = free}} with estimates for coastal and estuarine systems usually in the a lower range.

Ciliates constitute an important component of the microzooplankton community with preference for small-sized preys, in contrast to mesozooplankton, and many ciliate species are also grazed by mesozooplankton.{{cite journal |doi = 10.4319/lo.2000.45.8.1891|title = Zooplankton grazing and growth: Scaling within the 2-2,000-μm body size range|year = 2000|last1 = Hansen|first1 = Per Juel|last2 = Bjørnsen|first2 = Peter Koefoed|last3 = Hansen|first3 = Benni Winding|journal = Limnology and Oceanography|volume = 45|issue = 8|page = 1891|bibcode = 2000LimOc..45.1891H|doi-access = free}} Thus, ciliates can be an important link between small cells and higher trophic levels.{{cite journal |doi = 10.4319/lo.1994.39.3.0508|title = Regulation of zooplankton biomass and production in a temperate, coastal ecosystem. 2. Ciliates|year = 1994|last1 = Nielsen|first1 = Torkel Gissel|last2 = Kicrboe|first2 = Thomas|journal = Limnology and Oceanography|volume = 39|issue = 3|pages = 508–519|bibcode = 1994LimOc..39..508N|doi-access = free}} Besides their significant role in carbon transfer, ciliates are also considered high quality food, as a source of proteinaceous compounds with a low C:N ratio in comparison to phytoplankton.{{cite journal |doi = 10.1093/plankt/12.5.891|title = Predation on Protozoa: its importance to zooplankton|year = 1990|last1 = Stoecker|first1 = Diane K.|last2 = Capuzzo|first2 = Judith Mcdowell|journal = Journal of Plankton Research|volume = 12|issue = 5|pages = 891–908|doi-access = free}}{{cite journal |doi = 10.1111/j.1550-7408.1991.tb04806.x|title = The Protozoan-Metazoan Trophic Link in Pelagic Ecosystems|year = 1991|last1 = Gifford|first1 = Dian J.|journal = The Journal of Protozoology|volume = 38|pages = 81–86}}

File: Coleps-Konjugation.jpg sp.}} Two similar-looking but sexually distinct partners connected at their front ends exchange genetic material via a plasma bridge.]]

Although many ciliates are heterotrophs, a number of pelagic species are mixotrophic, combining both phagotrophic and phototrophic nutrition (Stoecker, 1998). The recognition of mixotrophy in the marine plankton food web has challenged the classical understanding of pelagic food webs, as autotrophy and heterotrophy are not necessarily two distinct functional compartments.{{cite journal |doi = 10.1093/plankt/fbs062|title = Misuse of the phytoplankton–zooplankton dichotomy: The need to assign organisms as mixotrophs within plankton functional types|year = 2013|last1 = Flynn|first1 = Kevin J.|last2 = Stoecker|first2 = Diane K.|last3 = Mitra|first3 = Aditee|last4 = Raven|first4 = John A.|last5 = Glibert|first5 = Patricia M.|author-link5=Patricia Glibert|last6 = Hansen|first6 = Per Juel|last7 = Granéli|first7 = Edna|last8 = Burkholder|first8 = Joann M.|journal = Journal of Plankton Research|volume = 35|pages = 3–11|doi-access = free}} Classical understanding of ecological interactions among plankton, such as competition for nutrients, indicates that nutrient uptake affinity decreases with organism size,{{cite journal |doi = 10.4319/lo.2012.57.2.0554|title = Allometric scaling and taxonomic variation in nutrient utilization traits and maximum growth rate of phytoplankton|year = 2012|last1 = Edwards|first1 = Kyle F.|last2 = Thomas|first2 = Mridul K.|last3 = Klausmeier|first3 = Christopher A.|last4 = Litchman|first4 = Elena|author-link4=Elena Litchman|journal = Limnology and Oceanography|volume = 57|issue = 2|pages = 554–566|bibcode = 2012LimOc..57..554E| s2cid=13376583 }} favoring smaller sizes under resource limiting conditions. Mixotrophy is advantageous to organisms under nutrient limited conditions, allowing them to reduce direct competition by grazing on smaller prey and increase direct ingestion of nutrients.{{cite journal |doi = 10.5194/bg-11-995-2014|title = The role of mixotrophic protists in the biological carbon pump|year = 2014|last1 = Mitra|first1 = A.|last2 = Flynn|first2 = K. J.|last3 = Burkholder|first3 = J. M.|last4 = Berge|first4 = T.|last5 = Calbet|first5 = A.|last6 = Raven|first6 = J. A.|last7 = Granéli|first7 = E.|last8 = Glibert|first8 = P. M.|last9 = Hansen|first9 = P. J.|last10 = Stoecker|first10 = D. K.|last11 = Thingstad|first11 = F.|last12 = Tillmann|first12 = U.|last13 = Våge|first13 = S.|last14 = Wilken|first14 = S.|last15 = Zubkov|first15 = M. V.|journal = Biogeosciences|volume = 11|issue = 4|pages = 995–1005|bibcode = 2014BGeo...11..995M|doi-access = free|hdl = 10261/93693|hdl-access = free}} Modeling results suggest that mixotrophy favors larger organisms, and therefore enhances trophic transfer efficiency.{{cite journal |doi = 10.1073/pnas.1517118113|title = Marine mixotrophy increases trophic transfer efficiency, mean organism size, and vertical carbon flux|year = 2016|last1 = Ward|first1 = Ben A.|last2 = Follows|first2 = Michael J.|journal = Proceedings of the National Academy of Sciences|volume = 113|issue = 11|pages = 2958–2963|pmid = 26831076|pmc = 4801304|bibcode = 2016PNAS..113.2958W|doi-access = free}} On top of that, mixotrophy appears to be important over both, space and time, in marine systems.{{cite journal |doi = 10.1098/rspb.2017.0664|title = Oceanic protists with different forms of acquired phototrophy display contrasting biogeographies and abundance|year = 2017|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.|last12 = Pitta|first12 = P.|last13 = Raven|first13 = J. A.|last14 = Johnson|first14 = M. D.|last15 = Glibert|first15 = P. M.|author-link15=Patricia Glibert|last16 = Våge|first16 = S.|journal = Proceedings of the Royal Society B: Biological Sciences|volume = 284|issue = 1860|pmid = 28768886|pmc = 5563798}} stressing the need for ecological field studies to further elucidate the role of mixotrophy.

File:Faure FremietTspCamp.jpg|Tintinnopsis campanula

File:Oxytricha chlorelligera - 400x (10403483023).jpg|Oxytricha chlorelligera

File:Stylonychia putrina - 160x - II (13215594964).jpg|Stylonychia putrina

File:Strombidium rassoulzadegani.jpg| The marine ciliate Strombidium rassoulzadegani

File:Holophyra ovum - 400x (9836710085).jpg|Holophyra ovum

File:Mikrofoto.de-Blepharisma japonicum 15.jpg|Blepharisma japonicum

File:Из жизни инфузорий.webm|Several taxa of ciliates interacting

File:Blepharisma americana.ogv|Blepharisma americanum swimming in a drop of pond water with other microorganisms

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| video1 = [https://www.youtube.com/watch?v=adHpXfepuWA&t=0s Peritrich Ciliates]

| video2 = [https://www.youtube.com/watch?v=Orw7xd2EqyM&ab_channel=JourneytotheMicrocosmos Conjugating protists]

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{{anchor|Macroscopic protists}}

File:Chaos carolinensis Wilson 1900.jpg|The single-celled giant amoeba has up to 1000 nuclei and reaches lengths of 5 mm.

File:Gromia in situ closeup.png|Gromia sphaerica is a large spherical testate amoeba which makes mud trails. Its diameter is up to 3.8 cm.{{cite journal|last = Matz|first = Mikhail V.|author2 = Tamara M. Frank|author3 = N. Justin Marshall|author4 = Edith A. Widder|author5 = Sonke Johnsen|title = Giant Deep-Sea Protist Produces Bilaterian-like Traces|journal = Current Biology|volume = 18|issue = 23|pages = 1849–1854|publisher = Elsevier Ltd|date = 2008-12-09|url = http://www.biology.duke.edu/johnsenlab/pdfs/pubs/sea%20grapes%202008.pdf|doi = 10.1016/j.cub.2008.10.028|pmid = 19026540| bibcode=2008CBio...18.1849M |s2cid = 8819675}}

File:Spiculosiphon oceana AB.png|Spiculosiphon oceana, a unicellular foraminiferan with an appearance and lifestyle that mimics a sponge, grows to 5 cm long.

File:Xenophyophore.jpg|The xenophyophore, another single-celled foraminiferan, lives in abyssal zones. It has a giant shell up to 20 cm across.{{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}}

File:Giant Kelp.jpg|Giant kelp, a brown algae, is not a true plant, yet it is multicellular and can grow to 50 m.

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File:Zooxanthellae.jpgs and coral]]

File:Planktonic protist interactome.webp Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].
Bipartite networks, providing an overview of the interactions represented by a manually curated Protist Interaction DAtabase (PIDA)}}]]

Interaction between microbial species has played important roles in evolution and speciation. One of the best examples is that the origin of eukaryotes is grounded in the interaction-events of endosymbiosis; giving rise to mitochondria, chloroplasts, and other metabolic capacities in the eukaryotic cell,{{Cite book|url=https://books.google.com/books?id=3sKzeiHUIUQC&q=%22Symbiosis+as+a+source+of+evolutionary+innovation%22|title = Symbiosis as a Source of Evolutionary Innovation: Speciation and Morphogenesis|isbn = 9780262132695|last1 = Margulis|first1 = Lynn|author-link = Lynn Margulis|last2 = Fester|first2 = René|year = 1991| publisher=MIT Press }}{{cite journal |doi = 10.1016/j.jtbi.2017.02.031|title = Symbiosis in eukaryotic evolution|year = 2017|last1 = López-García|first1 = Purificación|last2 = Eme|first2 = Laura|last3 = Moreira|first3 = David|journal = Journal of Theoretical Biology|volume = 434|pages = 20–33|pmid = 28254477|pmc = 5638015|bibcode = 2017JThBi.434...20L}}{{cite journal |doi = 10.1016/j.cub.2015.07.055|title = Endosymbiosis and Eukaryotic Cell Evolution|year = 2015|last1 = Archibald|first1 = John M.|journal = Current Biology|volume = 25|issue = 19|pages = R911–R921|pmid = 26439354|s2cid = 16089231|doi-access = free| bibcode=2015CBio...25.R911A }}{{cite journal |doi = 10.1146/annurev-ecolsys-110411-160320|title = Symbiogenesis: Mechanisms, Evolutionary Consequences, and Systematic Implications|year = 2013|last1 = Cavalier-Smith|first1 = Thomas|journal = Annual Review of Ecology, Evolution, and Systematics|volume = 44|pages = 145–172}} Microbial interactions guarantee ecosystem function, having crucial roles in, for instance, carbon channeling in photosymbiosis, control of microalgae blooms by parasites, and phytoplankton-associated bacteria influencing the growth and health of their host.

Despite their importance, understanding of microbial interactions in the ocean and other aquatic systems is rudimentary, and the majority of them are still unknown.{{cite journal |doi = 10.1038/s41559-017-0091|title = Parasites dominate hyperdiverse soil protist communities in Neotropical rainforests|year = 2017|last1 = Mahé|first1 = Frédéric|last2 = De Vargas|first2 = Colomban|last3 = Bass|first3 = David|last4 = Czech|first4 = Lucas|last5 = Stamatakis|first5 = Alexandros|last6 = Lara|first6 = Enrique|last7 = Singer|first7 = David|last8 = Mayor|first8 = Jordan|last9 = Bunge|first9 = John|last10 = Sernaker|first10 = Sarah|last11 = Siemensmeyer|first11 = Tobias|last12 = Trautmann|first12 = Isabelle|last13 = Romac|first13 = Sarah|last14 = Berney|first14 = Cédric|last15 = Kozlov|first15 = Alexey|last16 = Mitchell|first16 = Edward A. D.|last17 = Seppey|first17 = Christophe V. W.|last18 = Egge|first18 = Elianne|last19 = Lentendu|first19 = Guillaume|last20 = Wirth|first20 = Rainer|last21 = Trueba|first21 = Gabriel|last22 = Dunthorn|first22 = Micah|journal = Nature Ecology & Evolution|volume = 1|issue = 4|page = 91|pmid = 28812652| bibcode=2017NatEE...1...91M |s2cid = 2631960}}{{cite journal |doi = 10.1038/nature17652|title = In situ imaging reveals the biomass of giant protists in the global ocean|year = 2016|last1 = Biard|first1 = Tristan|last2 = Stemmann|first2 = Lars|last3 = Picheral|first3 = Marc|last4 = Mayot|first4 = Nicolas|last5 = Vandromme|first5 = Pieter|last6 = Hauss|first6 = Helena|last7 = Gorsky|first7 = Gabriel|last8 = Guidi|first8 = Lionel|last9 = Kiko|first9 = Rainer|last10 = Not|first10 = Fabrice|journal = Nature|volume = 532|issue = 7600|pages = 504–507|pmid = 27096373|bibcode = 2016Natur.532..504B|s2cid = 205248710|url = https://hal.sorbonne-universite.fr/hal-01324873/file/Biard_2016_In_situ_imaging.pdf}}{{cite journal |doi = 10.1023/A:1008879616066|title = Freshwater protozoa: Biodiversity and ecological function|year = 1998|last1 = Finlay|first1 = B.J.|last2 = Esteban|first2 = G.F.|journal = Biodiversity and Conservation|volume = 7|issue = 9|pages = 1163–1186| bibcode=1998BiCon...7.1163F |s2cid = 10702795}} The earliest surveys of interactions between aquatic microbes date back to the 19th century. In 1851, while on board HMS Rattlesnake in the Pacific Ocean, Thomas Huxley discovered small yellow–green cells inside the conspicuous planktonic radiolarians which he thought were organelles.{{cite journal |doi = 10.1080/03745486109495002|title = XXXIV.—Zoological notes and observations made on board H.M.S. Rattlesnake|year = 1851|last1 = Huxley|first1 = Thomas H.|journal = Annals and Magazine of Natural History|volume = 8|issue = 48|pages = 433–442|url = https://zenodo.org/record/2454610}} Later, Karl Brandt established the yellowish cells were symbiotic alga and named them zooxanthella.Brandt K. (1881) "Uber das Zusammenleben von Thieren und Algen". Verh Physiol Ges, 1: 524–527. Since these early studies, hundreds of others have reported microbial interactions by using classic tools, mainly microscopy, but this knowledge has not yet been gathered into one accessible database. In recent years the high throughput sequencing (HTS){{cite journal |doi = 10.1016/j.mimet.2012.07.017|title = Environmental microbiology through the lens of high-throughput DNA sequencing: Synopsis of current platforms and bioinformatics approaches|year = 2012|last1 = Logares|first1 = Ramiro|last2 = Haverkamp|first2 = Thomas H.A.|last3 = Kumar|first3 = Surendra|last4 = Lanzén|first4 = Anders|last5 = Nederbragt|first5 = Alexander J.|last6 = Quince|first6 = Christopher|last7 = Kauserud|first7 = Håvard|journal = Journal of Microbiological Methods|volume = 91|issue = 1|pages = 106–113|pmid = 22849829}}{{cite journal |doi = 10.1073/pnas.0605127103|title = Microbial diversity in the deep sea and the underexplored "rare biosphere"|year = 2006|last1 = Sogin|first1 = M. L.|last2 = Morrison|first2 = H. G.|last3 = Huber|first3 = J. A.|last4 = Welch|first4 = D. M.|last5 = Huse|first5 = S. M.|last6 = Neal|first6 = P. R.|last7 = Arrieta|first7 = J. M.|last8 = Herndl|first8 = G. J.|journal = Proceedings of the National Academy of Sciences|volume = 103|issue = 32|pages = 12115–12120|pmid = 16880384|pmc = 1524930|bibcode = 2006PNAS..10312115S|doi-access = free}}{{cite journal |doi = 10.1038/nrg.2016.49|title = Coming of age: Ten years of next-generation sequencing technologies|year = 2016|last1 = Goodwin|first1 = Sara|last2 = McPherson|first2 = John D.|last3 = McCombie|first3 = W. Richard|journal = Nature Reviews Genetics|volume = 17|issue = 6|pages = 333–351|pmid = 27184599|s2cid = 8295541|pmc = 10373632}} of environmental DNA or RNA has transformed understanding of microbial diversity{{hsp}}Pedrós-Alió C, Acinas SG, Logares R, Massana R. Marine microbial diversity as seen by high throughput sequencing. In: {{Cite book|url=https://books.google.com/books?id=fKJFDwAAQBAJ&q=%22Microbial+ecology+of+the+oceans%22|title = Microbial Ecology of the Oceans|isbn = 9781119107187|last1 = Gasol|first1 = Josep M.|last2 = Kirchman|first2 = David L.|date = 27 March 2018| publisher=John Wiley & Sons }}, pp. 47–87. and evolution,{{cite journal |doi = 10.1038/nature14447|title = Complex archaea that bridge the gap between prokaryotes and eukaryotes|year = 2015|last1 = Spang|first1 = Anja|last2 = Saw|first2 = Jimmy H.|last3 = Jørgensen|first3 = Steffen L.|last4 = Zaremba-Niedzwiedzka|first4 = Katarzyna|last5 = Martijn|first5 = Joran|last6 = Lind|first6 = Anders E.|last7 = Van Eijk|first7 = Roel|last8 = Schleper|first8 = Christa|last9 = Guy|first9 = Lionel|last10 = Ettema|first10 = Thijs J. G.|journal = Nature|volume = 521|issue = 7551|pages = 173–179|pmid = 25945739|pmc = 4444528|bibcode = 2015Natur.521..173S}} as well as generating hypotheses on microbial interactions based on correlations of estimated microbial abundances over spatiotemporal scales.{{cite journal |doi = 10.1016/j.mib.2015.04.004|title = Metagenomics meets time series analysis: Unraveling microbial community dynamics|year = 2015|last1 = Faust|first1 = Karoline|last2 = Lahti|first2 = Leo|last3 = Gonze|first3 = Didier|last4 = De Vos|first4 = Willem M.|last5 = Raes|first5 = Jeroen|journal = Current Opinion in Microbiology|volume = 25|pages = 56–66|pmid = 26005845|doi-access = free}}{{cite journal |doi = 10.1038/nrmicro2832|title = Microbial interactions: From networks to models|year = 2012|last1 = Faust|first1 = Karoline|last2 = Raes|first2 = Jeroen|journal = Nature Reviews Microbiology|volume = 10|issue = 8|pages = 538–550|pmid = 22796884|s2cid = 22872711}}{{cite journal |doi = 10.1126/science.1262073|title = Determinants of community structure in the global plankton interactome|year = 2015|last1 = Lima-Mendez|first1 = G.|last2 = Faust|first2 = K.|last3 = Henry|first3 = N.|last4 = Decelle|first4 = J.|last5 = Colin|first5 = S.|last6 = Carcillo|first6 = F.|last7 = Chaffron|first7 = S.|last8 = Ignacio-Espinosa|first8 = J. C.|last9 = Roux|first9 = S.|last10 = Vincent|first10 = F.|last11 = Bittner|first11 = L.|last12 = Darzi|first12 = Y.|last13 = Wang|first13 = J.|last14 = Audic|first14 = S.|last15 = Berline|first15 = L.|last16 = Bontempi|first16 = G.|last17 = Cabello|first17 = A. M.|last18 = Coppola|first18 = L.|last19 = Cornejo-Castillo|first19 = F. M.|last20 = d'Ovidio|first20 = F.|last21 = De Meester|first21 = L.|last22 = Ferrera|first22 = I.|last23 = Garet-Delmas|first23 = M.-J.|last24 = Guidi|first24 = L.|last25 = Lara|first25 = E.|last26 = Pesant|first26 = S.|last27 = Royo-Llonch|first27 = M.|last28 = Salazar|first28 = G.|last29 = Sanchez|first29 = P.|last30 = Sebastian|first30 = M.|journal = Science|volume = 348|issue = 6237|pmid = 25999517|s2cid = 10326640|display-authors = 1|hdl = 10261/117702|hdl-access = free}}{{cite journal |doi = 10.1016/j.tim.2016.11.008|title = Disentangling Interactions in the Microbiome: A Network Perspective|year = 2017|last1 = Layeghifard|first1 = Mehdi|last2 = Hwang|first2 = David M.|last3 = Guttman|first3 = David S.|journal = Trends in Microbiology|volume = 25|issue = 3|pages = 217–228|pmid = 27916383|pmc = 7172547}}

The diagram on the right is an overview of the interactions between planktonic protists recorded in a manually curated Protist Interaction DAtabase (PIDA). The network is based on 2422 ecological interactions in the PIDA registered from ~500 publications spanning the last 150 years. The nomenclature and taxonomic order of Eukaryota is based on Adl et al. 2019.{{cite journal |title = Revisions to the classification, nomenclature, and diversity of eukaryotes|year = 2019|doi = 10.1111/jeu.12691|doi-access = free|last1 = Adl|first1 = Sina M.|last2 = Bass|first2 = David|last3 = Lane|first3 = Christopher E.|last4 = Lukeš|first4 = Julius|last5 = Schoch|first5 = Conrad L.|last6 = Smirnov|first6 = Alexey|last7 = Agatha|first7 = Sabine|last8 = Berney|first8 = Cedric|last9 = Brown|first9 = Matthew W.|last10 = Burki|first10 = Fabien|last11 = Cárdenas|first11 = Paco|last12 = Čepička|first12 = Ivan|last13 = Chistyakova|first13 = Lyudmila|last14 = Campo|first14 = Javier|last15 = Dunthorn|first15 = Micah|last16 = Edvardsen|first16 = Bente|last17 = Eglit|first17 = Yana|last18 = Guillou|first18 = Laure|last19 = Hampl|first19 = Vladimír|last20 = Heiss|first20 = Aaron A.|last21 = Hoppenrath|first21 = Mona|last22 = James|first22 = Timothy Y.|last23 = Karnkowska|first23 = Anna|last24 = Karpov|first24 = Sergey|last25 = Kim|first25 = Eunsoo|last26 = Kolisko|first26 = Martin|last27 = Kudryavtsev|first27 = Alexander|last28 = Lahr|first28 = Daniel J.G.|last29 = Lara|first29 = Enrique|last30 = Le Gall|first30 = Line|journal = Journal of Eukaryotic Microbiology|volume = 66|issue = 1|pages = 4–119|pmid = 30257078|pmc = 6492006|display-authors = 1}} The nomenclature and taxonomic order of Bacteria is based on Schultz et al. 2017.{{cite journal |title = Towards a balanced view of the bacterial tree of life|year = 2017|doi = 10.1186/s40168-017-0360-9|doi-access = free|last1 = Schulz|first1 = Frederik|last2 = Eloe-Fadrosh|first2 = Emiley A.|last3 = Bowers|first3 = Robert M.|last4 = Jarett|first4 = Jessica|last5 = Nielsen|first5 = Torben|last6 = Ivanova|first6 = Natalia N.|last7 = Kyrpides|first7 = Nikos C.|last8 = Woyke|first8 = Tanja|journal = Microbiome|volume = 5|issue = 1|page = 140|pmid = 29041958|pmc = 5644168}}

The nodes are grouped (outer circle) according to eukaryotic supergroups (or Incertae sedis), Bacteria and Archaea. All major protistan lineages were involved in interactions as hosts, symbionts (mutualists and commensalists), parasites, predators, and/or prey. Predation was the most common interaction (39%), followed by symbiosis (29%), parasitism (18%), and unresolved interactions (14%, where it is uncertain whether the interaction is beneficial or antagonistic). Nodes represent eukaryotic and prokaryotic taxa and are colored accordingly. Node size indicates the number of edges/links that are connected to that node. Each node/taxon is assigned a number, which corresponds with the numbers for taxa in B, C and D. Edges represent interactions between two taxa and are colored according to ecological interaction type: predation (orange), symbiosis (green), and parasitism (purple).

The network is undirected, meaning that a node can contain both parasites/symbionts/prey and hosts/predators. To avoid cluttering of the figure, "Self-loops", which represent cases where both interacting organisms belong to the same taxon (e.g., a dinoflagellate eating another dinoflagellate) are not shown as edges/links in this figure, but are considered in the size of nodes. The outermost circle groups taxa in the different eukaryotic ‘supergroups’ or the prokaryotic domains Bacteria and Archaea. Ancryomonadidae is abbreviated An. Telonema is not placed into any of the supergroups, but classified as Incertae sedis (abbreviated I.S. in the figure). In B, B, and D the following abbreviations for supergroups are used: Ar Archaea, Ba Bacteria, Rh Rhizaria, Al Alveolata, St Stramenopiles, Ha Haptista, Cy Cryptista, Ap Archaeplastida, Ex Excavata, Ob Obazoa, Am Amoebozoa, Cu CRuMS, An Ancryomonadidae, Is Incertae sedis.

B: Predator–prey interactions in PIDA. The node numbers correspond to taxa node numbers in a. Abbreviations for supergroups are described above. Background and nodes are colored according to functional role in the interaction: Prey are colored light orange (left part of figure), while predators are depicted in dark orange (right part of figure). The size of each node represents the number of edges connected to that node.

C. Symbiont–host interactions included in PIDA. The node numbers correspond to node numbers in A. Abbreviations for supergroups are described above. Symbionts are to the left, colored light green, and their hosts are to the right in dark green. The size of each node represents the number of edges connected to that node.

D: Parasite–host interactions included in PIDA. The node numbers correspond to node numbers in A. Abbreviations for supergroups are described above. Parasite taxa are depicted in light purple (left), hosts in dark purple (right).

It was found that protist predators seem to be "multivorous" while parasite–host and symbiont–host interactions appear to have moderate degrees of specialization. The SAR supergroup (i.e., Stramenopiles, Alveolata, and Rhizaria) heavily dominated PIDA, and comparisons against a global-ocean molecular survey (Tara expedition) indicated that several SAR lineages, which are abundant and diverse in the marine realm, were underrepresented among the recorded interactions.

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{{main|Protist shell}}

{{see also|Protists in the fossil record}}

Many protists have protective shells or tests,{{Cite web|title=Groups of Protists {{!}} Boundless Biology|url=https://courses.lumenlearning.com/boundless-biology/chapter/groups-of-protists/|access-date=2021-02-16|website=courses.lumenlearning.com}} usually made from calcium carbonate (chalk) or silica (glass). Protists are mostly single-celled and microscopic. Their shells are often tough mineralised forms that resist degradation, and can survive the death of the protist as a microfossil. Although protists are very small, they are ubiquitous. Their numbers are such that their shells play a huge part in the formation of ocean sediments, and in the global cycling of elements and nutrients.

Diatom shells are called frustules and are made from silica. These glass structures have accumulated for over 100 million years leaving rich deposits of nano and microstructured silicon oxide in the form of diatomaceous earth around the globe. The evolutionary causes for the generation of nano and microstructured silica by photosynthetic algae are not yet clear. However, in 2018 it was shown that reflection of ultraviolet light by nanostructured silica protects the DNA in the algal cells, and this may be an evolutionary cause for the formation of the glass cages.De Tommasi, E., Congestri, R., Dardano, P., De Luca, A.C., Managò, S., Rea, I. and De Stefano, M. (2018) "UV-shielding and wavelength conversion by centric diatom nanopatterned frustules". Scientific Reports, 8(1): 1–14. {{doi|10.1038/s41598-018-34651-w}}. 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

Coccolithophores are protected by a shell constructed from ornate circular plates or scales called coccoliths. The coccoliths are made from calcium carbonate or chalk. The term coccolithophore derives from the Greek for a seed carrying stone, referring to their small size and the coccolith stones they carry.

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| caption1 = Diatoms, major components of marine plankton, have glass skeletons called frustules. "The microscopic structures of diatoms help them manipulate light, leading to hopes they could be used in new technologies for light detection, computing or robotics.[https://horizon-magazine.eu/article/biodegradable-glitter-and-pollution-eating-microalgae-new-materials-inspired-nature.html Biodegradable glitter and pollution-eating microalgae: the new materials inspired by nature] Horizon, 28 May 2020.

| image2 = SEM images of pores in diatom frustules.webp

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| caption2 = {{center|SEM images of pores in diatom frustulesAguirre, L.E., Ouyang, L., Elfwing, A., Hedblom, M., Wulff, A. and Inganäs, O. (2018) "Diatom frustules protect DNA from ultraviolet light". Scientific reports, 8(1): 1–6. {{doi|10.1038/s41598-018-21810-2}}. 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].}}

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| caption1 = Coccolithophores are armoured with chalk plates or stones called coccoliths. The images above show the size comparison between the relatively large coccolithophore Scyphosphaera apsteinii and the relatively small but ubiquitous Emiliania huxleyi.Gafar, N.A., Eyre, B.D. and Schulz, K.G. (2019) "A comparison of species specific sensitivities to changing light and carbonate chemistry in calcifying marine phytoplankton". Scientific Reports, 9(1): 1–12. {{doi|10.1038/s41598-019-38661-0}}. 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

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| caption1 = Benefits in coccolithophore calcification{{hsp}} – see text below

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| caption2 = Energetic costs in coccolithophore calcification{{hsp}}

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There are benefits for protists that carry protective shells. The diagram on the left above shows some benefits coccolithophore get from carrying coccoliths. In the diagram, (A) represents accelerated photosynthesis including carbon concentrating mechanisms (CCM) and enhanced light uptake via scattering of scarce photons for deep-dwelling species. (B) represents protection from photodamage including sunshade protection from ultraviolet light (UV) and photosynthetic active radiation (PAR) and energy dissipation under high-light conditions. (C) represents armour protection includes protection against viral/bacterial infections and grazing by selective and nonselective grazers.Monteiro, F.M., Bach, L.T., Brownlee, C., Bown, P., Rickaby, R.E., Poulton, A.J., Tyrrell, T., Beaufort, L., Dutkiewicz, S., Gibbs, S. and Gutowska, M.A. (2016) "Why marine phytoplankton calcify". Science Advances, 2(7): e1501822. {{doi|10.1126/sciadv.1501822}}. 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

There are also costs for protists that carry protective shells. The diagram on the right above shows some of the energetic costs coccolithophore incur from carrying coccoliths. In the diagram, the energetic costs are reported in percentage of total photosynthetic budget. (A) represents transport processes include the transport into the cell from the surrounding seawater of primary calcification substrates Ca₂+ and HCO₃− (black arrows) and the removal of the end product H+ from the cell (gray arrow). The transport of Ca₂+ through the cytoplasm to the coccolith vesicle (CV) is the dominant cost associated with calcification. (B) represents metabolic processes include the synthesis of coccolith-associated polysaccharides (CAPs – gray rectangles) by the Golgi complex (white rectangles) that regulate the nucleation and geometry of CaCO₃ crystals. The completed coccolith (gray plate) is a complex structure of intricately arranged CAPs and CaCO₃ crystals. (C) Mechanical and structural processes account for the secretion of the completed coccoliths that are transported from their original position adjacent to the nucleus to the cell periphery, where they are transferred to the surface of the cell.

• Cavalier-Smith's system of classification

{{reflist}}

• {{cite journal |doi = 10.1038/s41396-019-0542-5|title = The planktonic protist interactome: Where do we stand after a century of research?|year = 2020|last1 = Bjorbækmo|first1 = Marit F. Markussen|last2 = Evenstad|first2 = Andreas|last3 = Røsæg|first3 = Line Lieblein|last4 = Krabberød|first4 = Anders K.|last5 = Logares|first5 = Ramiro|journal = The ISME Journal|volume = 14|issue = 2|pages = 544–559|pmid = 31685936|pmc = 6976576| bibcode=2020ISMEJ..14..544B }} 50px Available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].
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• {{cite journal | last1=Keeling | first1=Patrick J. | last2=Campo | first2=Javier del | title=Marine Protists Are Not Just Big Bacteria | journal=Current Biology | publisher=Elsevier BV | volume=27 | issue=11 | year=2017 | issn=0960-9822 | doi=10.1016/j.cub.2017.03.075 | pages=R541–R549| pmid=28586691 | s2cid=207052528 | doi-access=free | bibcode=2017CBio...27.R541K }}

{{microorganisms|state=expanded}}

Category:Microorganisms

Category:Marine organisms

Category:Planktology

Category:Biological oceanography

Category:Marine biology

Category:Protists