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Protozoa (in Greek proto = first and zoa = animals) are unicellular eukaryotes, (singular protozoan). While there is no exact definition of the term, most scientists use protozoan to refer to a unicellular heterotrophic protist.

Characteristics

Most are around 10–50 μm, but forms up to 0.5 mm can easily be seen under a microscope. Protozoa are exsistent throughout aqueous environments and soil, but don't play an important role in their ecology. Protozoa occupy a range of trophic levels. As predators, they prey upon unicellular or filamentous algae, bacteria, and microfungi. Protozoa play a role both as herbivores and as consumers in the decomposer link of the food chain. Protozoa also play a vital role in controlling bacteria populations and biomass. As components of the micro- and meiofauna, protozoa are not an important food source for microinvertebrates. Thus, the ecological role of protozoain the transfer of bacterial and algal production to successive trophic levels is important. Protozoa such as the malaria parasites (Plasmodium spp.), trypanosomes and leishmania are also important as parasites and symbionts of multicellular animals.

Most protozoa exist in 5 stages of life which are in the form of trophozoites and cyst. When in the form of cysts, they are able to survive harsh conditions. They are able to survive exposure to extreme temperatures, harmful chemicals or without food, water, or oxygen for a period of time. In parasitic species, the cyst will also enable it to survive outside of the host, allowing it to be transferred from one host to another. An individual protozoan is both male and female. On the other hand, when protozoa are in the form of trophozoites (Greek, tropho=to nourish), they actively feed and grow. The process by which the protozoa takes its cyst form is called encystation, while the process of transforming back into trophozoite is called excystation.

Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce sexually, some asexually, and some both (eg. Coccidia).

Another name for protozoa is Acrita (R. Owen, 1861). It can also be considered Eukaryotic Cell Functionase.

Classification

Protozoans were commonly grouped in the kingdom of Protista together with the plant-like algae and fungus-like water molds and slime molds. In 21st-century systematics, however, most of the algae are classified in kingdoms such as Plantae and Chromista^{[citation needed]}; and in such cases the remaining life forms are occasionally classified as a kingdom Protozoa^{[citation needed]}. But the name is misleading, since protozoans are neither Animalia nor Metazoa (with the possible exception of the enigmatic, moldy Myxozoa)^{[citation needed]}.

Sub-Groups

Protozoa have traditionally been divided on the basis of their means of locomotion, although this is no longer believed to represent genuine relationships:

• Flagellates (eg. Giardia lambdia)
• Amoeboids (eg. Entamoeba histolytica)
• Sporozoans (eg. Plasmodium knowlesi)
  • Apicomplexa
  • Myxozoa
  • Microsporidia
• Ciliates (eg. Balantidium coli)

Photos

Map

Taxonomy

Phyla

Acrasiomycota

Acrasiomycota is a phylum of the Kingdom Discicristates related to protists. The name acrasio- comes from the Greek Akrasia, meaning "acting against one's better judgement." This group consists of cellular slime molds. [more]

At least 13 species and subspecies belong to the Phylum Acrasiomycota.

More info about the Phylum Acrasiomycota may be found here.

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]

At least 151 species and subspecies belong to the Phylum Amoebozoa.

More info about the Phylum Amoebozoa may be found here.

Apusozoa

At least 3 species and subspecies belong to the Phylum Apusozoa.

More info about the Phylum Apusozoa may be found here.

Cercozoa

At least 36 species and subspecies belong to the Phylum Cercozoa.

More info about the Phylum Cercozoa may be found here.

Choanozoa

Choanozoa (Greek: χόανος (choanos) = "funnel" + ζῶον (z�on) = "animal") is the name of a phylum of protists that belongs to the line of opisthokonts. [more]

At least 120 species and subspecies belong to the Phylum Choanozoa.

More info about the Phylum Choanozoa may be found here.

Ciliophora

At least 951 species and subspecies belong to the Phylum Ciliophora.

More info about the Phylum Ciliophora may be found here.

Dinophyta

The dinoflagellates 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. About half of all dinoflagellates are photosynthetic, and these make up the largest group of eukaryotic algae aside from the diatoms. Being primary producers make them an important part of the aquatic food chain. Some species, called zooxanthellae, are endosymbionts of marine animals and protozoa, 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]

At least 1,172 species and subspecies belong to the Phylum Dinophyta.

More info about the Phylum Dinophyta may be found here.

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 µm in size, although some euglenids get up to 500 µm long. [more]

At least 1,820 species and subspecies belong to the Phylum Euglenozoa.

More info about the Phylum Euglenozoa may be found here.

Foraminifera

The Foraminifera, ("Hole Bearers") or forams for short, are a large group of amoeboid protists with 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. About 275,000 species are recognized, both living and fossil.^{[citation needed]} They are usually less than 1 mm in size, but some are much larger, and the largest recorded specimen reached 19 cm.^{[citation needed]} [more]

At least 4,746 species and subspecies belong to the Phylum Foraminifera.

More info about the Phylum Foraminifera may be found here.

Heliozoa

At least 21 species and subspecies belong to the Phylum Heliozoa.

More info about the Phylum Heliozoa may be found here.

Heterokontophyta

More info about the Phylum Heterokontophyta may be found here.

Loukozoa

More info about the Phylum Loukozoa may be found here.

Metamonada

More info about the Phylum Metamonada may be found here.

Myxomycota

Myxomycota is a phylum of the Kingdom Amoebozoa related to protists. The name comes from the Greek Myxo, meaning "slime", and mycota, meaning fungus. They are also known as the plasmodial or acellular slime molds. [more]

At least 2,349 species and subspecies belong to the Phylum Myxomycota.

More info about the Phylum Myxomycota may be found here.

Myzozoa

At least 1,101 species and subspecies belong to the Phylum Myzozoa.

More info about the Phylum Myzozoa may be found here.

Percolozoa

More info about the Phylum Percolozoa may be found here.

Plasmodiophoromycota

The Phytomyxea are a group of protists that are parasites of plants. A more common name for them is the plasmodiophorids, but this does not always include Phagomyxa. They typically develop within plant cells, causing the infected tissue to grow into a gall or scab. Important diseases caused by phytomyxeans include club root in cabbage and its relatives, and powdery scab in potatoes. These are caused by species of Plasmodiophora and Spongospora, respectively. [more]

At least 66 species and subspecies belong to the Phylum Plasmodiophoromycota.

More info about the Phylum Plasmodiophoromycota may be found here.

Protozoa

Protozoa (in Greek proto = first and zoa = animals) are unicellular eukaryotes, (singular protozoan). While there is no exact definition of the term, most scientists use protozoan to refer to a unicellular heterotrophic protist. [more]

At least 3,320 species and subspecies belong to the Phylum Protozoa.

More info about the Phylum Protozoa may be found here.

Radiozoa

More info about the Phylum Radiozoa may be found here.

Sarcomastigophora

The phylum Sarcomastigophora includes many unicellular or colonial, autotrophic, or heterotrophic organisms. The two main sub-phyla are Mastigophora and Sarcodina. [more]

At least 1,435 species and subspecies belong to the Phylum Sarcomastigophora.

More info about the Phylum Sarcomastigophora may be found here.

Sources

• The text on this page is licensed under the GNU Free Documentation License. It includes material from Wikipedia retrieved Tuesday, April 22, 2008.
• The distribution map on this page comes from the Global Biodiversity Information Facility and is used with permission.
• Photographs on this page are copyrighted by individual photographers, and individual copyrights apply.
• The GMapImageCutter is used under license from the UCL Centre for Advanced Spatial Analysis.
• The technology underlying this page, including the Image Browser and controls behind Keep Exploring, is owned by the BayScience Foundation. All rights are reserved.