Six examples of protozoa (phagotrophic eukaryotes) that act as models. (a) Tetrahymena, a ciliate that has a versatile model role; image from the Open Access source. (b) The ciliates Paramecium and Didinium are used to evaluate predator–prey dynamics among other roles; image kindly provided by K. Hausmann. (c) Oxyrrhis is a marine flagellate that is emerging as model for a range of topics; image by D. Patterson and provided courtesy of microscope.mbl.edu. (d) Trypanosoma is a blood parasite that provides a source of mitochondria among other attributes; image rights obtained from Eye of Science. (e) Dictyostelium is a soil amoeba that is possibly the most important medical-model protozoon; image kindly provided by R.L. Blanton. (f) Monosiga is a choanoflagellate that is emerging as a model because of its phylogenetic affinity to metazoa; image kindly provided by the King Laboratory, UC Berkeley.