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ciliate
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but in general shorter and present in much larger numbers, with a different undulating pattern than flagella. Cilia occur in all members of the group (although the peculiar Suctoria only have them for part of the life-cycle) and are variously used in swimming, crawling, attachment, feeding, and sensation. Nevertheless, although not a general practice, some authors prefer to call "cilia" both eukaryotic cilia and flagella, reserving the term "flagella" to the bacterial structure. Anywise, the fundamental difference between multiciliate flagellates (e.g., hemimastigids, ''Stephanopogon'', ''Multicilia'', opalines) and ciliates is the presence of macronuclei in ciliates alone.〔Cavalier-Smith, T. (2000). Flagellate megaevolution: the basis for eukaryote diversification. In: Leadbeater, B.S.C., Green, J.C. (eds.). ''The Flagellates. Unity, diversity and evolution''. London: Taylor and Francis, pp. 361-390, p. 362, ().〕
Ciliates are an important group of protists, common almost everywhere there is water — in lakes, ponds, oceans, rivers, and soils. About 3,500 species have been described, and the potential number of extant species is estimated at 30,000.〔Adl, Sina M., et al. "Diversity, nomenclature, and taxonomy of protists." Systematic Biology 56.4 (2007): 685.〕 Included in this number are many ectosymbiotic and endosymbiotic species, as well as some obligate and opportunistic parasites. Ciliate species range in size from as little as 10 µm to as much as 4 mm in length, and include some of the most morphologically complex protozoans.〔Nielsen, Torkel Gissel, and Thomas Kiørboe. "Regulation of zooplankton biomass and production in a temperate, coastal ecosystem. 2. Ciliates." Limnology and Oceanography 39.3 (1994): 508-519.〕
In most systems of taxonomy, "Ciliophora" is ranked as a phylum,〔(【引用サイトリンク】url=http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=46211 )〕 under either the kingdom Protista or Protozoa. In some systems of classification, ciliated protozoa are placed within the class "Ciliata,"〔(【引用サイトリンク】title=Introduction to the Ciliata )〕〔(【引用サイトリンク】title=Ciliata — Definition from Merriam-Webster's Medical Dictionary )〕 (a term which can also refer to an unrelated genus of fish). In the taxonomic scheme proposed by the International Society of Protistologists, which eliminates formal rank designations such as "phylum" and "class", "Ciliophora" is an unranked taxon within Alveolata.〔Adl, Sina M., et al. "The new higher level classification of eukaryotes with emphasis on the taxonomy of protists." ''Journal of Eukaryotic Microbiology'' 52.5 (2005): 399-451.〕〔Adl, Sina M., et al. "The revised classification of eukaryotes." ''Journal of Eukaryotic Microbiology'' 59.5 (2012): 429-514.〕
==Cell structure==
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