Paulinella chromatophora Lauterborn, 1895
Diagnosis: shell pyroid or broad-elliptical, not compressed, composed of siliceous, rectanguloid plates with slightly rounded, scarcely overlapping borders, arranged in circumferential longitudinal rows; in apertural view the plates form a counter-clockwise spiral, with one pentagonal scale at the aboral pole. Pseudostome small. Cell with usually two organelles: sausage-like endosymbionts of cyanobacterial origin. Filopodia, usually fast moving.
Dimensions: 20-30 µm long, sometimes up to 40 µm.
Ecology: fresh water, between waterplants and in debris, sometimes in Sphagnum. Sometimes abundant in floating debris between blue algae in early spring.
Remarks: Paulinella chromatophora is a freshwater filose amoeba with photosynthetic endosymbionts (chromatophores) of cyanobacterial origin. 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. The P. chromatophora symbiont was related to the Prochlorococcus and Synechococcus cyanobacteria.