Description of Paulinella
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Test: ovoid, made of siliceous rectanguloid plates with slightly rounded, scarcely overlapping ends, arranged in transversely circumferential longitudinal rows, in apertural view the plates form a counter-clockwise spiral, one pentagonal scale at the aboral pole. All known species small (45 µm). Ultrastructure of plates with smooth surface but porous subsurface layer or internal channels with rows of pores differs from that of other Euglyphida. Pseudostome: on short neck. Paulinella chromatophora has two sausage like curved, short blue-green cyanobacteria as symbionts, no food vacuoles, 1 to 3 rapidly moving filopods. Habitat: freshwater plants, plankton but also brackish water and marine sediments; Molecular studies place this close to cercomonads. Type species, Paulinella chromatophora Lauterborn, 1895.
