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 differentundulating 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. All behavioral patterns are coordinated by signaling processes.
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. Included in this number are many ectosymbiotic and endosymbiotic species, as well as some obligate andopportunistic 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.
In most systems of taxonomy, “Ciliophora” is ranked as a phylum, under either the kingdom Protista orProtozoa. In some systems of classification, ciliated protozoa are placed within the class “Ciliata,” (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 unrankedtaxon within Alveolata.
(From Wikipedia, June 2016)