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: Test 20-30 µm long, sometimes up to 40 µm.

Ecology: Fresh water, between aquatic plants 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.

Click here for further reading about the ancestors of Paulinella.

Nicholls (2009) describes six new marine species.