Learn Online about Marine Animals
These are single celled animals. Protozoans comprise a large and diverse group of microscopic organisms that live as single cells or in simple colonies. Some of them can produce elaborate shells that eventually sink and form large deposits at the bottom of the sea. They are divided into five protist phyla: Mastigophora (the flagellates), Sarcodina (the amebas), Ciliophora (the ciliates), Opalinida, and Sporozoa. Most are motile and most ingest food. The 26,000 living species are found in freshwater and at all depths in the ocean. Some are even parasites in the bodies of humans or other animals, sometimes causing diseases.