Ciliate

Ciliate

Karyorelictea
Heterotrichea
Spirotrichea
Litostomatea
Phyrea
Plagiopylea
See text for subclasses.

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 typically 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.

Ciliates are one of the most important groups of protists, common almost everywhere there is water — in lakes, ponds, oceans, rivers, and soils. Ciliates have many ectosymbiotic and endosymbiotic members, as well as some obligate and opportunistic parasites. Ciliates are large single cells, a few reaching 2 mm in length, and are some of the most complex protozoans in structure.

The term "Ciliophora" is used in classification as a phylum. Ciliophora can be classified under Protista or Protozoa. The term "Ciliata" is also used, as a class. (However, this latter term can also refer to a type of fish.) Protista classification is rapidly evolving, and it is not rare to encounter these terms used to describe other hierarchical levels.