Invertebrate Zoology/Protozoans

thumb|This protozoan was collected in a pond in Quebec. One of the earliest forms forms of life, protozoans have simple body plans and are always single-celled, like the protozoan depicted to the right. Protozoans exist as individuals, but some are colonial. All the metabolic activities of an organism like respiration, digestion, excretion and reproduction are carried out by these single celled organisms.