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{{Short description|Diverse motile unicellular heterotrophic eukaryotic organisms}}File:Protozoa collage 2.jpg|right|thumb|upright=1.5|Clockwise from top left: Blepharisma japonicum, a ciliate; Giardia muris, a parasitic flagellate; Centropyxis aculeata, a testate (shelled) amoeba; Peridinium willei, a dinoflagellate; Chaos carolinense, a naked amoebozoan; Desmerella moniliformis, a choanoflagellatechoanoflagellateProtozoa (also protozoan, plural protozoans) is an informal term for single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris.BOOK,weblink The Cell: Evolution of the First Organism, Panno, Joseph, 14 May 2014, Infobase Publishing, 9780816067367, en, BOOK,weblink Environmental Microbiology: Fundamentals and Applications: Microbial Ecology, Bertrand, Jean-Claude, Caumette, Pierre, Lebaron, Philippe, Matheron, Robert, Normand, Philippe, Sime-Ngando, Télesphore, 2015-01-26, Springer, 9789401791182, en, Historically, the protozoa were regarded as "one-celled animals", because they often possess animal-like behaviors, such as motility and predation, and lack a cell wall, as found in plants and many algae.BOOK,weblink Brock Biology of Microorganisms, Madigan, Michael T., 2012, Benjamin Cummings, 9780321649638, BOOK,weblink Protozoa: Structure, Classification, Growth, and Development, Yaeger, Robert G., 1996, NCBI, 2018-03-23, 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.In some systems of biological classification, Protozoa is a high-level taxonomic group. When first introduced in 1818, Protozoa was erected as a taxonomic class, but in later classification schemes it was elevated to a variety of higher ranks, including phylum, subkingdom and kingdom. In a series of classifications proposed by Thomas Cavalier-Smith and his collaborators since 1981, Protozoa has been ranked as a kingdom.JOURNAL, Cavalier-Smith, Thomas, Tom Cavalier-Smith, 1981, Eukaryote kingdoms: seven or nine?, Bio Systems, 14, 3–4, 461–481, 10.1016/0303-2647(81)90050-2, 7337818, JOURNAL, Cavalier-Smith, Thomas, Tom Cavalier-Smith, December 1993, Kingdom protozoa and its 18 phyla, Microbiological Reviews, 57, 4, 953–994, 372943, 8302218, JOURNAL, Cavalier-Smith, Thomas, Tom Cavalier-Smith, 23 June 2010, Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree, Biology Letters, 6, 3, 342–345, 10.1098/rsbl.2009.0948, 2880060, 20031978, The seven-kingdom scheme presented by Ruggiero et al. in 2015, places eight phyla under Kingdom Protozoa: Euglenozoa, Amoebozoa, Metamonada, Choanozoa sensu Cavalier-Smith, Loukozoa, Percolozoa, Microsporidia and Sulcozoa. Notably, this kingdom excludes several major groups of organisms traditionally placed among the protozoa, including the ciliates, dinoflagellates, foraminifera, and the parasitic apicomplexans, all of which are classified under Kingdom Chromista. Kingdom Protozoa, as defined in this scheme, does not form a natural group or clade, but a paraphyletic group or evolutionary grade, within which the members of Fungi, Animalia and Chromista are thought to have evolved.


File:Georg_August_Goldfuss_Protozoa_Infusoria_Monades.jpg|left|thumb|upright=1.35|Class Protozoa, order Infusoria, family Monades by Georg August GoldfussGeorg August GoldfussThe word "protozoa" (singular protozoon or protozoan) was coined in 1818 by zoologist Georg August Goldfuss, as the Greek equivalent of the German , meaning "primitive, or original animals" (}} ‘proto-’ + }} ‘animal’). Goldfuss created Protozoa as a class containing what he believed to be the simplest animals.JOURNAL, Goldfuß, Ueber die Classification der Zoophyten, Isis, Oder, Encyclopädische Zeitung von Oken, 1818, 2, 6, 1008–1019,weblink On the classification of zoophytes, German, From p. 1008: "Erste Klasse. Urthiere. Protozoa." (First class. Primordial animals. Protozoa.) [Note: each column of each page of this journal is numbered; there are two columns per page.] Originally, the group included not only single-celled microorganisms but also some "lower" multicellular animals, such as rotifers, corals, sponges, jellyfish, bryozoa and polychaete worms.BOOK, Goldfuß, Georg August, Handbuch der Zoologie. Erste Abtheilung., Handbook of Zoology. First Part., 1820, Johann Leonhard Schrag, Nürnberg, (Germany), XI–XIV,weblink German, The term Protozoa is formed from the Greek words {{wikt-lang|grc|πρῶτος}} ({{grc-transl|πρῶτος}}), meaning "first", and {{wikt-lang|grc|ζῶα}} ({{grc-transl|ζῶα}}), plural of {{wikt-lang|grc|ζῶον}} ({{grc-transl|ζῶον}}), meaning "animal".BOOK, Abrégé du dictionnaire grec français, Bailly, Anatole, 1981-01-01, Hachette, 978-2010035289, Paris, 461974285, WEB,weblink Greek-french dictionary online, Bailly, Anatole,, 2018-10-05, The use of Protozoa as a formal taxon has been discouraged by some researchers, mainly because the term implies kinship with animals (Metazoa)JOURNAL, Hogg, John, John Hogg, 1860, On the distinctions of a plant and an animal, and on a fourth kingdom of nature,weblink Edinburgh New Philosophical Journal, 2nd series, 12, 216–225, JOURNAL, Scamardella, J. M., December 1999, Not plants or animals: a brief history of the origin of Kingdoms Protozoa, Protista and Protoctista, International Microbiology, 2, 4, 207–216, 10943416, and promotes an arbitrary separation of "animal-like" from "plant-like" organisms.JOURNAL, Copeland, Herbert F., September–October 1947, Progress Report on Basic Classification, The American Naturalist, 81, 800, 340–361, 10.1086/281531, 2458229, In 1848, as a result of advancements in cell theory pioneered by Theodor Schwann and Matthias Schleiden, the anatomist and zoologist C. T. von Siebold proposed that the bodies of protozoans such as ciliates and amoebae consisted of single cells, similar to those from which the multicellular tissues of plants and animals were constructed. Von Siebold redefined Protozoa to include only such unicellular forms, to the exclusion of all metazoa (animals).BOOK, Siebold (vol. 1), Stannius (vol. 2), Lehrbuch der vergleichenden Anatomie [Textbook of Comparative Anatomy], 1848, Veit & Co., Berlin, (Germany), vol. 1: Wirbellose Thiere (Invertebrate animals), 3,weblink German, From p. 3: "Erste Hauptgruppe. Protozoa. Thiere, in welchen die verschiedenen Systeme der Organe nicht scharf ausgeschieden sind, und deren unregelmässige Form und einfache Organisation sich auf eine Zelle reduziren lassen." (First principal group. Protozoa. Animals, in which the different systems of organs are not sharply separated, and whose irregular form and simple organization can be reduced to one cell.) At the same time, he raised the group to the level of a phylum containing two broad classes of microorganisms: Infusoria (mostly ciliates and flagellated algae), and Rhizopoda (amoeboid organisms). The definition of Protozoa as a phylum or sub-kingdom composed of "unicellular animals" was adopted by the zoologist Otto Bütschli—celebrated at his centenary as the "architect of protozoology"JOURNAL, Dobell, C., April 1951, In memoriam Otto Bütschli (1848-1920) "architect of protozoology", Isis; an International Review Devoted to the History of Science and Its Cultural Influences, 42, 127, 20–22, 14831973, 10.1086/349230, —and the term came into wide use.File:John_Hogg_--_Primigenum_or_Protoctista.jpg|thumb|upright=1.35|John Hogg's illustration of the Four Kingdoms of Nature, showing "Primigenal" as a greenish haze at the base of the Animals and Plants, 1860]]As a phylum under Animalia, the Protozoa were firmly rooted in the old "two-kingdom" classification of life, according to which all living beings were classified as either animals or plants. As long as this scheme remained dominant, the protozoa were understood to be animals and studied in departments of Zoology, while photosynthetic microorganisms and microscopic fungi—the so-called Protophyta—were assigned to the Plants, and studied in departments of Botany.JOURNAL, Taylor, F. J. R. 'Max', 11 January 2003, The collapse of the two-kingdom system, the rise of protistology and the founding of the International Society for Evolutionary Protistology (ISEP),weblink International Journal of Systematic and Evolutionary Microbiology, 53, 6, 1707–1714, 10.1099/ijs.0.02587-0, 14657097, Criticism of this system began in the latter half of the 19th century, with the realization that many organisms met the criteria for inclusion among both plants and animals. For example, the algae Euglena and Dinobryon have chloroplasts for photosynthesis, but can also feed on organic matter and are motile. In 1860, John Hogg argued against the use of "protozoa", on the grounds that "naturalists are divided in opinion—and probably some will ever continue so—whether many of these organisms, or living beings, are animals or plants." As an alternative, he proposed a new kingdom called Primigenum, consisting of both the protozoa and unicellular algae (protophyta), which he combined together under the name "Protoctista". In Hoggs's conception, the animal and plant kingdoms were likened to two great "pyramids" blending at their bases in the Kingdom Primigenum.Six years later, Ernst Haeckel also proposed a third kingdom of life, which he named Protista. At first, Haeckel included a few multicellular organisms in this kingdom, but in later work he restricted the Protista to single-celled organisms, or simple colonies whose individual cells are not differentiated into different kinds of tissues.Despite these proposals, Protozoa emerged as the preferred taxonomic placement for heterotrophic microorganisms such as amoebae and ciliates, and remained so for more than a century. In the course of the 20th century, however, the old "two kingdom" system began to weaken, with the growing awareness that fungi did not belong among the plants, and that most of the unicellular protozoa were no more closely related to the animals than they were to the plants. By mid-century, some biologists, such as Herbert Copeland, Robert H. Whittaker and Lynn Margulis, advocated the revival of Haeckel's Protista or Hogg's Protoctista as a kingdom-level eukaryotic group, alongside Plants, Animals and Fungi. A variety of multi-kingdom systems were proposed, and Kingdoms Protista and Protoctista became well established in biology texts and curricula.JOURNAL, Whittaker, R. H., 10 January 1969, New concepts of kingdoms or organisms. Evolutionary relations are better represented by new classifications than by the traditional two kingdoms, Science, 163, 3863, 150–160, 1969Sci...163..150W, 10.1126/science.163.3863.150, 5762760,, BOOK, Margulis, Lynn, Lynn Margulis, 1974, Springer, 978-1-4615-6946-6, Dobzhansky, Theodosius, 45–78, Hecht, Max K., Steere, William C., 10.1007/978-1-4615-6944-2_2, Five-Kingdom Classification and the Origin and Evolution of Cells, Evolutionary Biology, JOURNAL, Cavalier-Smith, Thomas, Tom Cavalier-Smith, August 1998, A revised six-kingdom system of life, Biological Reviews, 73, 3, 203–266, 10.1111/j.1469-185X.1998.tb00030.x, 9809012, While many taxonomists have abandoned Protozoa as a high-level group, Thomas Cavalier-Smith has retained it as a kingdom in the various classifications he has proposed. As of 2015, Cavalier-Smith's Protozoa excludes several major groups of organisms traditionally placed among the protozoa, including the ciliates, dinoflagellates and foraminifera (all members of the SAR supergroup). In its current form, his kingdom Protozoa is a paraphyletic group which includes a common ancestor and most of its descendants, but excludes two important clades that branch within it: the animals and fungi.JOURNAL, Ruggiero, Michael A., Gordon, Dennis P., Orrell, Thomas M., Bailly, Nicolas, Bourgoin, Thierry, Brusca, Richard C., Cavalier-Smith, Thomas, Tom Cavalier-Smith, Guiry, Michael D., Kirk, Paul M., 29 April 2015, A Higher Level Classification of All Living Organisms, PLoS ONE, 10, 4, e0119248, 2015PLoSO..1019248R, 10.1371/journal.pone.0119248, 4418965, 25923521, Since the protozoa, as traditionally defined, can no longer be regarded as "primitive animals" the terms "protists", "Protista" or "Protoctista" are sometimes preferred. In 2005, members of the Society of Protozoologists voted to change its name to the International Society of Protistologists.WEB,weblink New President's Address,, 1 May 2015,



Protozoa, as traditionally defined, range in size from as little as 1 micrometre to several millimetres, or more.BOOK,weblink Dictionary of microbiology and molecular biology, Singleton, Paul, Sainsbury, Diana, 2001, Wiley, 9780471941507, en, Among the largest are the deep-sea–dwelling xenophyophores, single-celled foraminifera whose shells can reach 20 cm in diameter.JOURNAL, Gooday, A.J., Aranda da Silva, A. P., Pawlowski, J., Xenophyophores (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic), Deep-Sea Research Part II: Topical Studies in Oceanography, 1 December 2011, 58, 24–25, 2401–2419, 2011DSRII..58.2401G, 10.1016/j.dsr2.2011.04.005, (File:Spirostomum.jpeg|thumb|The ciliate Spirostomum ambiguum can attain 3 mm in length){| class="wikitable"!Species !Cell type!Size in micrometres
Plasmodium falciparum >malaria parasite, trophozoite phaseHTTP://WWW.MICROBIOLOGYBOOK.ORG/PARASITOLOGY/BLOOD-MALARIA.HTMLAST=GHAFFARDATE=ARCHIVE-URL=DEAD-URL=, 2018-03-23, |1-2
Bodo saltans >Kinetoplastida>kinetoplastid flagellateMITCHELL>FIRST=GARY C.FIRST2=J. H.FIRST3=M. A. TITLE=FEEDING OF A FRESHWATER FLAGELLATE, BODO SALTANS, ON DIVERSE BACTERIA VOLUME=35 PAGES=219–222, 10.1111/j.1550-7408.1988.tb04327.x, |5-8
Entamoeba histolytica >amoebozoanHTTPS://MSU.EDU/COURSE/ZOL/316/EHISSCOPE.HTM ENTAMOEBA HISTOLYTICA>WEBSITE=MSU.EDU, 2016-08-21, |15–60
Balantidium coli >LAST=LEHMAN WEBSITE=UNIVERSITY OF DELAWARE, 2018-03-23, |50-100
Paramecium caudatum >PARAMECIUM CAUDATUM>LAST=TAYLORDATE=ARCHIVE-URL=DEAD-URL=, 2018-03-23, |120-330
Amoeba proteus >AMOEBA PROTEUS {{!, Microworld>|access-date=2016-08-21}}|220–760
Syringammina fragilissima >| foraminiferan amoeboid200000}}


Free-living protozoans are common and often abundant in fresh, brackish and salt water, as well as other moist environments, such as soils and mosses. Some species thrive in extreme environments such as hot springsBOOK,weblink Seen and Unseen: Discovering the Microbes of Yellowstone, Sheehan, Kathy B., 2005, Falcon, 9780762730933, en, and hypersaline lakes and lagoons.JOURNAL, Post, F. J., Borowitzka, L. J., Borowitzka, M. A., Mackay, B., Moulton, T., 1983-09-01, The protozoa of a Western Australian hypersaline lagoon, Hydrobiologia, en, 105, 1, 95–113, 10.1007/BF00025180, 0018-8158, 2004HyBio.524..167W, All protozoa require a moist habitat; however, some can survive for long periods of time in dry environments, by forming resting cysts which enable them to remain dormant until conditions improve.Parasitic and symbiotic protozoa live on or within other organisms, including vertebrates and invertebrates, as well as plants and other single-celled organisms. Some are harmless or beneficial to their host organisms; others may be significant causes of diseases, such as babesia, malaria and toxoplasmosis.File:Isotricha intestinalis.jpg|thumb|Isotricha intestinalisIsotricha intestinalisAssociation between protozoan symbionts and their host organisms can be mutually beneficial. Flagellated protozoans such as Trichonympha and Pyrsonympha inhabit the guts of termites, where they enable their insect host to digest wood by helping to break down complex sugars into smaller, more easily digested molecules.WEB,weblink Termite gut microbes {{!, NOLL LAB||language=en|access-date=2018-03-21}} A wide range of protozoans live commensally in the rumens of ruminant animals, such as cattle and sheep. These include flagellates, such as Trichomonas, and ciliated protozoa, such as Isotricha and Entodinium.BOOK, The Rumen Microbial Ecosystem, Williams, A. G., Coleman, G. S., 1997, Springer, Dordrecht, 9789401071499, 73–139, 10.1007/978-94-009-1453-7_3, The ciliate subclass Astomatia is composed entirely of mouthless symbionts adapted for life in the guts of annelid worms.BOOK,weblink An illustrated guide to the protozoa: organisms traditionally referred to as protozoa, or newly discovered groups, Lee, John J., Leedale, Gordon F., Bradbury, Phyllis Clarke, 25 May 2000, Society of Protozoologists, 634, en,


All protozoans are heterotrophic, deriving nutrients from other organisms, either by ingesting them whole or consuming their organic remains and waste-products. Some protozoans take in food by phagocytosis, engulfing organic particles with pseudopodia (as amoebae do), or taking in food through a specialized mouth-like aperture called a cytostome. Others take in food by osmotrophy, absorbing dissolved nutrients through their cell membranes.{{cn|date=September 2018}}Parasitic protozoans use a wide variety of feeding strategies, and some may change methods of feeding in different phases of their life cycle. For instance, the malaria parasite Plasmodium feeds by pinocytosis during its immature trophozoite stage of life (ring phase), but develops a dedicated feeding organelle (cytostome) as it matures within a host's red blood cell.WEB,weblink Biochemistry of Plasmodium, Wiser, Mark F., The Wiser Page, 2018-03-22, File:Ameba_001.jpg|thumb|Paramecium bursaria, a ciliate which derives some of its nutrients from algal endosymbionts in the genus ChlorellaChlorellaProtozoa may also live as mixotrophs, supplementing a heterotrophic diet with some form of autotrophy. Some protozoa form close associations with symbiotic photosynthetic algae, which live and grow within the membranes of the larger cell and provide nutrients to the host. Others practice kleptoplasty, stealing chloroplasts from prey organisms and maintaining them within their own cell bodies as they continue to produce nutrients through photosynthesis. The ciliate Mesodinium rubrum retains functioning plastids from the cryptophyte algae on which it feeds, using them to nourish themselves by autotrophy. These, in turn, may be passed along to dinoflagellates of the genus Dinophysis , which prey on Mesodinium rubrum but keep the enslaved plastids for themselves. Within Dinophysis, these plastids can continue to function for months.JOURNAL, Nishitani, Goh, Nagai, Satoshi, Baba, Katsuhisa, Kiyokawa, Susumu, Kosaka, Yuki, Miyamura, Kazuyoshi, Nishikawa, Tetsuya, Sakurada, Kiyonari, Shinada, Akiyoshi, May 2010, High-Level Congruence of Myrionecta rubra Prey and Dinophysis Species Plastid Identities as Revealed by Genetic Analyses of Isolates from Japanese Coastal Waters, Applied and Environmental Microbiology, 76, 9, 2791–2798, 10.1128/AEM.02566-09, 2863437, 20305031,


Organisms traditionally classified as protozoa are abundant in aqueous environments and soil, occupying a range of trophic levels. The group includes flagellates (which move with the help of whip-like structures called flagella), ciliates (which move by using hair-like structures called cilia) and amoebae (which move by the use of foot-like structures called pseudopodia). Some protozoa are sessile, and do not move at all.


Unlike plants, fungi and most types of algae, protozoans do not typically have a rigid cell wall, but are usually enveloped by elastic structures of membranes that permit movement of the cell. In some protozoans, such as the ciliates and euglenozoans, the cell is supported by a composite membranous envelope called the "pellicle". The pellicle gives some shape to the cell, especially during locomotion. Pellicles of protozoan organisms vary from flexible and elastic to fairly rigid. In ciliates and Apicomplexa, the pellicle is supported by closely packed vesicles called alveoli. In euglenids, it is formed from protein strips arranged spirally along the length of the body. Familiar examples of protists with a pellicle are the euglenoids and the ciliate Paramecium. In some protozoa, the pellicle hosts epibiotic bacteria that adhere to the surface by their fimbriae (attachment pili).Protozoa in biological research (File:Dileptus_viridis_cyst.jpg|thumb|Resting cyst of ciliated protozoan Dileptus viridis.)

Life cycle

(File:Toxoplasmosis life cycle en.svg|thumb|Life cycle of parasitic protozoan, Toxoplasma gondii)Some protozoa have two-phase life cycles, alternating between proliferative stages (e.g., trophozoites) and dormant cysts. As cysts, protozoa can survive harsh conditions, such as exposure to extreme temperatures or harmful chemicals, or long periods without access to nutrients, water, or oxygen for periods of time. Being a cyst enables parasitic species to survive outside of a host, and allows their transmission from one host to another. When protozoa are in the form of trophozoites (Greek tropho = to nourish), they actively feed. The conversion of a trophozoite to cyst form is known as encystation, while the process of transforming back into a trophozoite is known as excystation.All protozoans reproduce (not all) asexually by binary fission or multiple fission. Many protozoan species exchange genetic material by sexual means (typically, through conjugation); however, sexuality is generally decoupled from the process of reproduction, and does not immediately result in increased population.WEB,weblink Sex and Death in Protozoa, Cambridge University Press, 2015-06-09, Although meiotic sex is widespread among present day eukaryotes, it has, until recently, been unclear whether or not eukaryotes were sexual early in their evolution. Due to recent advances in gene detection and other techniques, evidence has been found for some form of meiotic sex in an increasing number of protozoans of ancient lineage that diverged early in eukaryotic evolution.Bernstein H, Bernstein C (2013). Bernstein C, Bernstein H eds. Evolutionary Origin and Adaptive Function of Meiosis'. Meiosis. InTech. {{ISBN|978-953-51-1197-9}} (See eukaryote reproduction.) Thus, such findings suggest that meiotic sex arose early in eukaryotic evolution. Examples of protozoan meiotic sexuality are described in the articles Amoebozoa, Giardia lamblia, Leishmania, Plasmodium falciparum biology, Paramecium, Toxoplasma gondii, Trichomonas vaginalis and Trypanosoma brucei.


{{Further|wikispecies:Protozoa}}Historically, the Protozoa were classified as "unicellular animals", as distinct from the Protophyta, single-celled photosynthetic organisms (algae) which were considered primitive plants. Both groups were commonly given the rank of phylum, under the kingdom Protista.BOOK,weblink Protozoology, Kudo, Richard R. (Richard Roksabro), 1954, Springfield, Ill., C. C. Thomas, MBLWHOI Library, In older systems of classification, the phylum Protozoa was commonly divided into several sub-groups, reflecting the means of locomotion.JOURNAL, Honigberg, B. M., W. Balamuth, E. C. Bovee, J. O. Corliss, M. Gojdics, R. P. Hall, R. R. Kudo, N. D. Levine, A. R. Lobblich, February 1964, A Revised Classification of the Phylum Protozoa, Journal of Eukaryotic Microbiology, 11, 1, 7–20, 10.1111/j.1550-7408.1964.tb01715.x, J. Weiser, Classification schemes differed, but throughout much of the 20th century the major groups of Protozoa included: With the emergence of molecular phylogenetics and tools enabling researchers to directly compare the DNA of different organisms, it became evident that, of the main sub-groups of Protozoa, only the ciliates (Ciliophora) formed a natural group, or monophyletic clade (that is, a distinct lineage of organisms sharing common ancestry). The other classes or subphyla of Protozoa were all polyphyletic groups composed of organisms that, despite similarities of appearance or way of life, were not necessarily closely related to one another. In the system of eukaryote classification currently endorsed by the International Society of Protistologists, members of the old phylum Protozoa have been distributed among a variety of supergroups.JOURNAL, Adl, Sina M., Simpson, Alastair G. B., Lane, Christopher E., Lukeš, Julius, Bass, David, Bowser, Samuel S., Brown, Matthew W., Burki, Fabien, Dunthorn, Micah, 2012-09-01, The Revised Classification of Eukaryotes, Journal of Eukaryotic Microbiology, 59, 5, 429–514, 10.1111/j.1550-7408.2012.00644.x, 23020233, 3483872,


As components of the micro- and meiofauna, protozoa are an important food source for microinvertebrates. Thus, the ecological role of protozoa in the transfer of bacterial and algal production to successive trophic levels is important. As predators, they prey upon unicellular or filamentous algae, bacteria, and microfungi. Protozoan species include both herbivores and consumers in the decomposer link of the food chain. They also control bacteria populations and biomass to some extent.


File:Trophozoites_of_Entamoeba_histolytica_with_ingested_erythrocytes.JPG|thumb|Trophozoites of the amoebic dysentery pathogen Entamoeba histolytica with ingested human red blood cellred blood cellA number of protozoan pathogens are human parasites, causing diseases such as malaria (by Plasmodium), amoebiasis, giardiasis, toxoplasmosis, cryptosporidiosis, trichomoniasis, Chagas disease, leishmaniasis, African trypanosomiasis (sleeping sickness), amoebic dysentery, acanthamoeba keratitis, and primary amoebic meningoencephalitis (naegleriasis).The protozoan Ophryocystis elektroscirrha is a parasite of butterfly larvae, passed from female to caterpillar. Severely infected individuals are weak, unable to expand their wings, or unable to eclose, and have shortened lifespans, but parasite levels vary in populations. Infection creates a culling effect, whereby infected migrating animals are less likely to complete the migration. This results in populations with lower parasite loads at the end of the migration.JOURNAL, Bartel, Rebecca, Oberhauser, Karen, Karen Oberhauser, De Roode, Jacob, Atizer, Sonya, February 2011, Monarch butterfly migration and parasite transmission in eastern North America, Ecology, 92, 2, 342–351, 10.1890/10-0489.1, 21618914, This is not the case in laboratory or commercial rearing, where after a few generations, all individuals can be infected.JOURNAL, Leong, K. L. H., M. A. Yoshimura, H. K. Kaya, H. Williams, January 1997, Instar Susceptibility of the Monarch Butterfly (Danaus plexippus) to the Neogregarine Parasite, Ophryocystis elektroscirrha, Journal of Invertebrate Pathology, 69, 1, 79–83, 10.1006/jipa.1996.4634, 9028932,,




  • Dogiel, V. A., revised by J.I. Poljanskij and E. M. Chejsin. General Protozoology, 2nd ed., Oxford University Press, 1965.
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  • Sleigh, M. The Biology of Protozoa. E. Arnold: London, 1981.

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  • Lee, J.J., Leedale, G.F. & Bradbury, P. An Illustrated Guide to the Protozoa. Lawrence, Kansas, U.S.A: Society of Protozoologists, 2000; 2nd ed.
  • Patterson, D.J. Free-Living Freshwater Protozoa. A Colour Guide. Manson Publishing; London, 1996.
  • Patterson, D.J., M.A. Burford. A Guide to the Protozoa of Marine Aquaculture Ponds. CSIRO Publishing, 2001.

  • Harrison, F.W., Corliss, J.O. (ed.). 1991. Microscopic Anatomy of Invertebrates, vol. 1, Protozoa. New York: Wiley-Liss, 512 pp.
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Physiology and biochemistry
  • Nisbet, B. 1984. Nutrition and feeding strategies in Protozoa. Croom Helm Publ., London, 280 pp.
  • Coombs, G.H. & North, M. 1991. Biochemical protozoology. Taylor & Francis, London, Washington.
  • Laybourn-Parry J. 1984. A Functional Biology of Free-Living Protozoa. Berkeley, California: University of California Press.
  • Levandowski, M., S.H. Hutner (eds). 1979. Biochemistry and physiology of protozoa. Volumes 1, 2, and 3. Academic Press: New York, NY; 2nd ed.
  • Sukhareva-Buell, N.N. 2003. Biologically active substances of protozoa. Dordrecht: Kluwer.

  • Capriulo, G.M. (ed.). 1990. Ecology of Marine Protozoa. Oxford Univ. Press, New York.
  • Darbyshire, J.F. (ed.). 1994. Soil Protozoa. CAB International: Wallingford, U.K. 2009 pp.
  • Laybourn-Parry, J. 1992. Protozoan plankton ecology. Chapman & Hall, New York. 213 pp.
  • Fenchel, T. 1987. Ecology of protozoan: The biology of free-living phagotrophic protists. Springer-Verlag, Berlin. 197 pp.

  • Kreier, J.P. (ed.). 1991-1995. Parasitic Protozoa, 2nd ed. 10 vols (1-3 coedited by Baker, J.R.). Academic Press, San Diego, California, weblink.

  • Lee, J. J., & Soldo, A. T. (1992). Protocols in protozoology. Kansas, USA: Society of Protozoologists, Lawrence, weblink.

External links

  • EB1911, Protozoa,
{{Infectious disease}}{{Eukaryota classification}}{{Protozoa protist}}{{Taxonbar|from=Q101274}}{{Authority control}}

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