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The protozoa are one-celled animals and the smallest of all animals. Most of them can only be seen under a microscope. They do breathe, move, and reproduce like multicelled animals. They live in water or at least where it is damp. Animals in this group include the paramecium, the euglena and the amoeba.
Some protozoans are harmful to man as they can cause serious diseases. Others are helpful because they eat harmful bacteria and are food for fish and other animals.
Below is a link to a description of three types of protozoa.