Overview
Protozoa are a diverse group of unicellular eukaryotic organisms,1] many of which are motile. Originally, protozoa had been defined as unicellular protists with animal-like behavior, e.g., movement. Protozoa were regarded as the partner group of protists to protophyta, which have plant-like behaviour, e.g., photosynthesis.
Terminology
Following the Greek root of the name, the singular form is protozoon /pro?t?'zo?.?n/. Its use has, however, partially been replaced by the word protozoan, which was originally only used as an adjective. In the same manner the plural form protozoans is sometimes being used instead of protozoa.
In general, protozoa are referred to as animal-like protists because of movement (motile). However, both protozoa and protists are paraphyletic groups (not including all genetic relatives of the group). For example, Entamoeba is more closely related to humans than to Euglena. "Protozoa" is considered an outdated classification in more formal contexts. However, the term is still used in children's education.[2]
While there is no exact definition for the term protozoa, it often refers to a unicellular heterotrophic protist, such as the amoeba and ciliates. The term algae is used for microorganisms that photosynthesize. However, the distinction between protozoa and algae is often vague. For example, the algae Dinobryon has chloroplasts for photosynthesis, but it can also feed on organic matter and is motile.
Protozoa is sometimes considered a subkingdom.[3] It was traditionally considered a phylum under Animalia.[4]
Characteristics
Protozoa commonly range from 10 to 52 micrometers, but can grow as large as 1 mm, and are seen easily by microscope. The largest protozoa known are the deep-sea dwelling xenophyophores, which can grow up to 20 cm in diameter.
They were considered formerly to be part of the protista family. Protozoa exist throughout aqueous environments and soil, occupying a range of trophic levels.
Motility and digestion
Tulodens are one of the slow-moving form of protozoa. They move around with whip-like tails called flagella, hair-like structures called cilia, or foot-like structures called pseudopodia. Others do not move at all.
Protozoa may absorb food via their cell membranes, some, e.g., amoebas, surround food and engulf it, and yet others have openings or "mouth pores" into which they sweep food. All protozoa digest their food in stomach-like compartments called vacuoles.[5]
Ecological role
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. Protozoa are both herbivores and consumers in the decomposer link of the food chain. They also control bacteria populations and biomass to some extent. Protozoa such as the malaria parasites (Plasmodium spp.), trypanosomes and leishmania, are also important as parasites and symbionts of multicellular animals.
Life cycle
Some protozoa have life stages 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 a period 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.
Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce sexually, some asexually, while some use a combination, (e.g., Coccidia). An individual protozoan is hermaphroditic.
Classification
Protozoa were previously often grouped in the kingdom of Protista, together with the plant-like algae and fungus-like slime molds. As a result of 21st-century systematics, protozoa, along with ciliates, mastigophorans, and apicomplexans, are arranged as animal-like protists. With the possible exception of Myxozoa, protozoa are not categorized as Metazoa.[6] Protozoa are unicellular organisms and are often called the animal-like protists because they subsist entirely on other organisms for food. Most protozoa can move about on their own. Amoebas, Paramecia, and Trypanosomes are all examples of animal-like Protists.
Sub-groups
The classification of protozoa has been and remains a problematic area of taxonomy. Where th ey are available DNA sequences are used as the basis for classification but for the majority of described protozoa such material is not available. They have been and still are mostly on the basis of the their morphology and for the parasitic species their hosts.
Protozoa have been divided traditionally[citation needed] on the basis of their means of locomotion.
- Flagellates (e.g., Giardia lamblia)
- Amoeboids (e.g., Entamoeba histolytica)
- Sporozoans (e.g., Plasmodium knowlesi)
- Apicomplexa
- Myxozoa
- Microsporidia
- Ciliates (e.g., Balantidium coli)
As a phylum the Protozoa had been divided into four subphyla[7] reflecting the means of locomotion:
- Subphylum Sarcomastigophora
- Superclass Mastigophora (includes flagellates)
- Superclass Sarcodina (includes amoeboids)
- Superclass Opalinata
- Subphylum Sporozoa (includes apicomplexans)
- Subphylum Cnidospora
- Class Myxosporidea
- Class Microsporidea
- Subphylum Ciliophora (includes ciliates)
These classification systems are no longer considered to be valid.
Human disease
Some protozoa are human parasites, causing diseases.
Examples of human diseases caused by protozoa:
- Malaria
- Amoebiasis
- Giardiasis
- Toxoplasmosis
- Cryptosporidiosis
- Trichomoniasis
- Chagas disease
- Leishmaniasis
- Sleeping Sickness
- Dysentery
Life cycle
Some protozoa have life stages 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 a period 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.
Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce sexually, some asexually, while some use a combination, (e.g., Coccidia). An individual protozoan is hermaphroditic.
Classification
Protozoa were previously often grouped in the kingdom of Protista, together with the plant-like algae and fungus-like slime molds. As a result of 21st-century systematics, protozoa, along with ciliates, mastigophorans, and apicomplexans, are arranged as animal-like protists. With the possible exception of Myxozoa, protozoa are not categorized as Metazoa.[6] Protozoa are unicellular organisms and are often called the animal-like protists because they subsist entirely on other organisms for food. Most protozoa can move about on their own. Amoebas, Paramecia, and Trypanosomes are all examples of animal-like Protists.
Sub-groups
The classification of protozoa has been and remains a problematic area of taxonomy. Where they are available DNA sequences are used as the basis for classification but for the majority of described protozoa such material is not available. They have been and still are mostly on the basis of the their morphology and for the parasitic species their hosts.
Protozoa have been divided traditionally[citation needed] on the basis of their means of locomotion.
- Flagellates (e.g., Giardia lamblia)
- Amoeboids (e.g., Entamoeba histolytica)
- Sporozoans (e.g., Plasmodium knowlesi)
- Apicomplexa
- Myxozoa
- Microsporidia
- Ciliates (e.g., Balantidium coli)
As a phylum the Protozoa had been divided into four subphyla[7] reflecting the means of locomotion:
- Subphylum Sarcomastigophora
- Superclass Mastigophora (includes flagellates)
- Superclass Sarcodina (includes amoeboids)
- Superclass Opalinata
- Subphylum Sporozoa (includes apicomplexans)
- Subphylum Cnidospora
- Class Myxosporidea
- Class Microsporidea
- Subphylum Ciliophora (includes ciliates)
These classification systems are no longer considered to be valid.
Human disease
Some protozoa are human parasites, causing diseases.
Examples of human diseases caused by protozoa:
- Malaria
- Amoebiasis
- Giardiasis
- Toxoplasmosis
- Cryptosporidiosis
- Trichomoniasis
- Chagas disease
- Leishmaniasis
- Sleeping Sickness
- Dysentery
References
- ^ I. Edward Alcamo; Jennifer M. Warner (28 August 2009). Schaum's Outline of Microbiology. McGraw Hill Professional. pp. 144?. ISBN 9780071623261. http://books.google.com/books?id=nzvthLbcH6EC&pg=PA144. Retrieved 14 November 2010.
- ^ Michelle Gunter (1 January 2008). Passing the North Carolina 8th Grade End of Grade Test of Science. American Book Company, Inc.. pp. 196?. ISBN 9781598071863. http://books.google.com/books?id=pfUqvi1AJmMC&pg=PA196. Retrieved 14 November 2010.
- ^ "Protozoa" at Dorland's Medical Dictionary
- ^ Prof. R.L.Kotpal. Modern Text Book of Zoology: Invertebrates. Rastogi Publications. pp. 151?. ISBN 9788171339037. http://books.google.com/books?id=o7x7Zztp-5AC&pg=PA151. Retrieved 14 November 2010.
- ^ "Protozoa". MicrobeWorld. American Society for Chemistry. 2006. Archived from the original on 19 May 008. http://web.archive.org/web/20080519091815/http://www.microbeworld.org/microbes/protista/protozoa.aspx. Retrieved 15 June 2008.
- ^ Smothers et al, Science, 16 September 1994, "Molecular evidence that the myxozoan protists are metazoans", 8 June 2010
- ^ 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, J. Weiser (1964). "A Revised Classification of the Phylum Protozoa". Journal of Eukaryotic Microbiology 11 (1): 7?20. doi:10.1111/j.1550-7408.1964.tb01715.x.
Taxonomy
The Kingdom Protozoa is a member of the Domain Eukaryota. Here is the complete "parentage" of Protozoa:
The Kingdom Protozoa is further organized into finer groupings including:
- Subkingdom (2): Biciliata · Sarcomastigota
- Branch (1): Protostomia
- Infrakingdom (3): Alveolata · Excavata · Rhizaria
- Phylum (20): Acrasiomycota · Amoebozoa · Apusozoa · Cercozoa · Choanozoa · Ciliophora · Dinophyta · Euglenozoa · Foraminifera · Heliozoa · Heterokontophyta · Loukozoa · Metamonada · Myxomycota · Myzozoa · Percolozoa · Plasmodiophoromycota · Protozoa · Radiozoa · Sarcomastigophora
- Species: ZipcodeZoo has pages for 17,015 species and subspecies in the Kingdom Protozoa.
Phyla
Acrasiomycota
Acrasidae is a family of slime molds which belongs to the protist group Percolozoa. The name acrasio- comes from the Greek Akrasia, meaning "acting against one's judgement." This group consists of cellular slime molds. [more]
Amoebozoa
The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means of internal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like, called lobopodia. Most are unicellular, and are common in soils and aquatic habitats, with some found as symbiotes of other organisms, including several pathogens. The Amoebozoa also include the slime moulds, multinucleate or multicellular forms that produce spores and are usually visible to the unaided eye. [more]
Apusozoa
Cercozoa
Choanozoa
Choanozoa (Greek: (choanos) = "funnel" + ???? (zoon) = "animal") is the name of a phylum of protists that belongs to the line of opisthokonts. [more]
Ciliophora
Dinophyta
The dinoflagellates (Greek d???? dinos "whirling" and Latin flagellum "whip, scourge") are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth. Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey . Dinoflagellates are the largest group of marine eukaryotes aside from the diatoms. Being primary producers makes them an important part of the aquatic food chain. Some species, called zooxanthellae, are endosymbionts of marine animals and play an important part in the biology of coral reefs. Other dinoflagellates are colorless predators on other protozoa, and a few forms are parasitic (see for example Oodinium, Pfiesteria). [more]
Euglenozoa
The Euglenozoa are a large group of flagellate protozoa. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. There are two main subgroups, the euglenids and kinetoplastids. Euglenozoa are unicellular, mostly around 15-40 ?m in size, although some euglenids get up to 500 ?m long. [more]
Foraminifera
The Foraminifera ("hole bearers"), or forams for short, are a large phylum of amoeboid protists. They are among the most common marine plankton species. Forams have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net. They typically produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure. These shells are made of calcium carbonate (CaCO3) or agglutinated sediment particles. About 275,000 species are recognized, both living and fossil. They are usually less than 1 mm in size, but some are much larger, the largest species reaching up to 20 cm. [more]
Heliozoa
Heterokontophyta
Loukozoa
Metamonada
Myxomycota
Myxogastria (formely known as Myxomycota) is a class of Mycetozoa, itself a grouping of slime molds, that contains 5 orders, 14 families, 62 genera, and 888 species. Notable examples within Myxogastria include the genus Stemonitis and the species Physarum polycephalum. Myxogastria are also referred to as myxogastrids. [more]
Myzozoa
Myzozoa is a grouping of Alveolata, that feed through myzocytosis. [more]
Percolozoa
Plasmodiophoromycota
The Phytomyxea are a class of protists that are parasites of plants. It is divided into the orders Plasmodiophorida and Phagomyxida. A more common name for them is the plasmodiophorids, but this does not always include Phagomyxa (see taxobox). [more]
Protozoa
Protozoa are a diverse group of unicellular eukaryotic organisms, many of which are motile. Originally, protozoa had been defined as unicellular protists with animal-like behavior, e.g., movement. Protozoa were regarded as the partner group of protists to protophyta, which have plant-like behaviour, e.g., photosynthesis. [more]
Radiozoa
Radiolarians (also radiolaria) are amoeboid protozoa (diameter 0.1-0.2 mm) that produce intricate mineral skeletons, typically with a central capsule dividing the cell into inner and outer portions, called endoplasm and ectoplasm. They are found as zooplankton throughout the ocean, and their skeletal remains cover large portions of the ocean bottom as radiolarian ooze. Due to their rapid turn-over of species, they represent an important diagnostic fossil found from the Cambrian onwards. Some common radiolarian fossils include , Heliosphaera and Hexadoridium. [more]
Sarcomastigophora
The phylum Sarcomastigophora belongs to the Protist kingdom and it includes many unicellular or colonial, autotrophic, or heterotrophic organisms. [more]
At least 880 species and subspecies belong to the Phylum Sarcomastigophora.
More info about the Phylum Sarcomastigophora may be found here.
References
- ^ I. Edward Alcamo; Jennifer M. Warner (28 August 2009). Schaum's Outline of Microbiology. McGraw Hill Professional. pp. 144?. ISBN 9780071623261. http://books.google.com/books?id=nzvthLbcH6EC&pg=PA144. Retrieved 14 November 2010.
- ^ Michelle Gunter (1 January 2008). Passing the North Carolina 8th Grade End of Grade Test of Science. American Book Company, Inc.. pp. 196?. ISBN 9781598071863. http://books.google.com/books?id=pfUqvi1AJmMC&pg=PA196. Retrieved 14 November 2010.
- ^ "Protozoa" at Dorland's Medical Dictionary
- ^ Prof. R.L.Kotpal. Modern Text Book of Zoology: Invertebrates. Rastogi Publications. pp. 151?. ISBN 9788171339037. http://books.google.com/books?id=o7x7Zztp-5AC&pg=PA151. Retrieved 14 November 2010.
- ^ "Protozoa". MicrobeWorld. American Society for Chemistry. 2006. Archived from the original on 19 May 008. http://web.archive.org/web/20080519091815/http://www.microbeworld.org/microbes/protista/protozoa.aspx. Retrieved 15 June 2008.
- ^ Smothers et al, Science, 16 September 1994, "Molecular evidence that the myxozoan protists are metazoans", 8 June 2010
- ^ 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, J. Weiser (1964). "A Revised Classification of the Phylum Protozoa". Journal of E ukaryotic Microbiology 11 (1): 7?20. doi:10.1111/j.1550-7408.1964.tb01715.x.
Sources
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