ABSTRACT
The protozoa (proto = first; zoa = animals) are the animals that explored unicellularity. Animals, as opposed to plants, are primarily specialized to ingest particulate food. According to this definition, tapeworms and other parasites that live on dissolved rather than particulate food are not proper animals, but the word "primarily" implies that these parasites evolved from phagotrophic, i.e., particle-ingesting ancestors.
