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 endosymbiosis events). The P. chromatophora symbiont was related to the Prochlorococcus and Synechococcus cyanobacteria (sister to the group consisting of the living members of those two genera). Other than the symbiont, P. chromatophora is closely related to the heterotrophic P. ovalis.

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