INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

PROTISTS - PROTISTA

Protists are eukaryotic organisms with a unicellular level of Organization, lacking cellular differentiation and tissue formation. They comprise Protozoans, unicellular Algae, and zoosporic Fungi. Currently, about 120,000 species of protists are known, though their actual number in the biosphere is significantly larger.

Previously, protists were classified as a separate kingdom, on par with the kingdoms of plants, animals, and fungi. However, recent decades of research have proven that protists are a heterogeneous, collective group of eukaryotes with no distinct boundaries between protists and other eukaryotes. Consequently, a prevailing trend in modern Taxonomy is the transition to recognizing multiple kingdoms among which all protist phyla are distributed. Numerous diverse classifications are proposed, changing very rapidly. Therefore, we are compelled to adopt a provisional, considerably simplified system that combines traditional concepts with the latest achievements in biological science.

This textbook examines those protists characterized by an animal-like type of Cell organization and heterotrophic Nutrition, while retaining the traditional designation of Protozoa. The system of Protozoa is presented in a slightly modified form following S. A. Karpov (2005).