This article is about the protozoan. For the Austrailian doom metal band, see Paramaecium

Paramecium is a well-known genus of ciliate protozoa, commonly studied as a representative of that group. Paramecia are unicellular and slipper-shaped, ranging from 50 to 300 μm in length, depending on species. Simple cilia cover the body, and there is a deep oral groove, containing inconspicuous compound oral cilia, as found in other peniculids. Osmoregulation is carried out by a pair of contractile vacuoles, which actively expel water absorbed by osmosis from the surroundings. Paramecia are widespread in freshwater environments, and are especially common in scums. Paramecia are attracted by acidic conditions. Paramicia usually reproduce asexually, however, when food supplies are low, they may reproduce through a form of conjugation.

The division into species is still in flux—for instance, P. aurelia has recently been divided into 14 species—but the following are representative:

• P. aurelia Ehrenberg, 1838
• Paramecium bursaria (Ehrenberg) Focker, 1836
• P. calkinsi Woodruff, 1921
• P. caudatum Ehrenberg, 1838
• P. duboscqui Chatton and Brachon, 1933
• P. jenningsi Diller & Earl, 1958
• P. multimicronucleatum Powers & Mitchell, 1910
• P. nephridiatum von Gelei, 1925
• P. polycaryum Woodruff, 1923
• P. putrinum Claparede & Lachmann, 1858
• P. trichium Stokes, 1885
• P. woodruffi Wenrich, 1928

A number of doubtful species have also been recorded.

Ciliates

Paramecium in popular culture

• In a popular computer program, Chip's Challenge, the main character encounters a cartoon paramecium, one of the many monsters that he must overcome.

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