Paulinella is a genus of about nine species of freshwater amoeboids. Its most famous member is the photosynthetic P. chromatophora which has recently (evolutionarily speaking) taken on a cyanobacterium as an endosymbiont. This is striking because the chloroplasts of all other known photosynthetic eukaryotes derive ultimately from a single cyanobacterium endosymbiont which was taken in probably over a billion years ago in plants (and subsequently adopted into other eukaryote groups, by further e… (More on Paulinella)