Ice algae terrestrial ice algae occur in freshwater systems, the species composition differs greatly from that of sea ice algae. These communities are significant in that they often change the color of glaciers and ice sheets, impacting the reflectivity of the ice itself. Microbial life in sea ice is extremely diverse, and includes abundant algae, bacteria and protozoa. Algae in particular dominate the sympagic environment, with estimates of more than 1000 unicellular eukaryotes found to associate with sea ice in the Arctic. Species composition and diversity vary based on location, ice type, and irradiance. In general, pennate diatoms such as "Nitschia frigida"
Cavalier-Smith's system of classification distinguishes chromists from plants. Cavalier-Smith's eighth kingdom, Archezoa is now defunct. He now assigns former members of the kingdom Archezoa to the phylum Amoebozoa. Cavalier-Smith referred to what remained of the protist kingdom, after he removed the kingdoms Archezoa and Chromista, as the "kingdom Protozoa". In 1993, this kingdom contained 18 phyla as summarized in the following table: The phylum Opalozoa was established by Cavalier-Smith in 1991. By 1998, Cavalier-Smith had reduced the total number of kingdoms from eight to six: Animalia, Protozoa, Fungi, Plantae (including red and green algae), Chromista and Bacteria. Five of Cavalier-Smith's kingdoms are classified as