Protistan phylogeny and eukaryogenesis.
Publisher Summary This chapter focuses on the nature of the protists themselves, a group deserving much attention today if for no other reason then for their suitability as model cells in experimental researches of diverse kinds and discusses approaches to a better understanding of their phylogenetic interrelationships. The three principal ways of treating the protists systematically/evolutionarily are illustrated diagrammatically. While recognition of the prokaryote–eukaryote division made possible the whole idea of (and even the word, of course) eukaryogenesis, it did not directly help focus taxonomic attention on the protists. Protista are eukaryotic organisms with no more than one true tissue at most. The majority are unicellular in organization and microscopic in size. Even in macroscopic multicellular species (e.g., brown algae), clearly differentiated tissue stages may be considered absent, and no vascular forms exist. Motile species (via flagella, cilia, or pseudopodia) are common and widespread among most groups.