The species Carchesium on an activated sludge particle of the sewage
plant of Oldenburg. The cells without appendix are about 50 Ám in length.
Members of genus Vorticella represent one of the most impressive group within the Protozoa. They occur in nature as single organisms as well as in colonies looking like a bunch of flowers. They are ubiquitary in freshwater and seawater habitats where their favorite food, bacteria, occur in high concentrations. The micrograph shows an activated sludge sample of a sewage plant. Vorticella has cleared the water from small free-living bacteria while filamentous bacteria are too big to be get sucked in.

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