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The following points highlight the twelve characters of ciliated protozoans.
(i) Ciliates are protozoan protists which develop a number of cilia during a part or whole of the life cycle.
(ii) Cilia are used for locomotion and driving food.
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(iii) There is a high degree of morphological and physiological specialization.
(iv) Most ciliates are free living individuals in fresh and marine waters. A few are parasites.
(v) The body is covered by a pellicle.
(vi) Nutrition is holozoic except in the parasitic forms.
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(vii) There are definite regions for ingestion and egestion. The region of ingestion consists of an oral groove, cytostome (mouth) and gullet.
(viii) Ciliates show nuclear dimorphism or two types of nuclei, larger macronucleus (= mega nucleus) and smaller micronucleus. Macronucleus controls metabolic activities and growth. It is also called vegetative nucleus. Micronucleus takes part in reproduction. Hence, it is termed as reproductive nucleus.
(ix) Ciliates often possess minute ejectable trichocysts for defence.
(x) They have contractile vacuoles for osmoregulation.
(xi) Asexual reproduction takes place by transverse binary fission or budding. Cyst formation occurs under un-favourable conditions.
(xii) Sexual reproduction is by means of conjugation.
