Single-celled animals

Single-celled animals (Animalia) belong to the Sub regnum Protozoa – Phylum Protozoa. Just like the simple plants, the Protozoa are part of the plankton – animal plankton = zooplankton. Plankton does not move by itself, but is transported by the flow of the water. In the single cell animals all bodily functions are carried out in a single cell – they do not have specialized cells as bigger animals have. Protozoa feed on a variety of organic substances from the water. Some absorb the substances directly from the water, while others actively feed on bacteria or catch other protozoa. In some cases multiple one-celled animals live in a sort of colony as a group of loosely aggregated cells. Both in fresh and in salt water there are large numbers of protozoa in many different forms.