Protists are major components of phylogenetic diversity of eukaryotes. Most eukaryote groups are not multicellular, but unicellular algae and protozoans. Thus the information on the phylogenetic diversity of protists is important and essential to understand the evolution of eukaryotes. I addition, algae and protozoans are also important to understand aquatic ecosystems. About a half of the net production on the earth is carried by algae, and the main consumers of them are protozoans. Although the studies on the biodiversity of protists are important as mentioned above, we have only limited information. Even if you collect a protist from a pond in the university, it may be a new species. We study the phylogeny and taxonomy of various protists based on the ultrastructural and molecular approaches.
Phylogenetic tree of life. Familiar muulticellular organisms are limited to the Metazoa, Fungi and a part of Viridiplantae (green plants). All other eukaryotes are protists.