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Description of ParameciumPeniculine ciliates. Buccal opening located at the base of a groove of channel that starts at the front of the cell. There are no specialised cilia in the groove, but there are 4 peniculi within the mouth. The body is evenly ciliated except at the posterior end where there is a tuft of longer cilia. Bodies are cylindrical or more truncated (foot-shaped). Body surface underlain with extrusomes (trichocysts). With a single large central macronucleus and one or more micronuclei. With two contractile vacuoles, in most species the contractile vacuoles have radiating collecting canals. One or two species have symbiotic green algae. Eat bacteria. Common and widespread in freshwater habitats. Traditional species distinguished by body shape and configuration of the nuclei ï¿½ especially the micronuclei which may be single and large or small, vesiculate and more numerous. The Paramecium aurelia-group has been subdivided into such distinct genetic species by Sonneborn in 1975; other species groups are likely to be subdivided in the future. For animation of contractile vacuole complex, click on the image.