Cell diversification in heterotrophic flagellates

Abstract Heterotrophic flagellates are tremendously diverse. This chapter aims: (1) to outline my recent ideas on the higher classification of heterotrophic flagellates from the perspective of an eight kingdom system; (2) to outline the most probable phylogenetic relationships of heterotrophic flagellates; and (3) to discuss the radical steps in eukaryote cell evolution and diversification that created the major differences among the 15 phyla that contain heterotrophic flagellates. I argue that the first eukaryote was a heterotrophic and phagotrophic flagellate. The most fundamental steps in eukaryote evolution occurred either in heterotrophic flagellates or during their conversion into other types of eukaryote. These steps include the symbiotic origin of mitochondria and of chloroplasts. Heterotrophic flagellates are either primitively heterotrophic (most) and form a paraphyletic assemblage directly descended from the first eukaryote flagellates which had neither mitochondria nor chloroplasts, or they are derived from photosynthetic eukaryotes by the loss of plastids.