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Genus Paulinella

Shell is ovoid, covered with siliceous rectangular plates with slightly rounded, scarcely overlapping ends, arranged in circumferential longitudinal rows; in apertural view the plates form a counter-clockwise spiral, with one pentagonal scale at the aboral pole. Aperture is terminal or suberminal, circular or oval, sometimes located on the end of a small neck. Cytoplasm usually contains two sausage-like endosymbionts of cyanobacterial origin. Ecology: marine, brackish water and freshwater plants. Type species: Paulinella chromatophora Lauterborn, 1895