STUDIES ON THE GENERA GYROSIGMA AND PLEUROSIGMA (BACILLARIOPHYCEAE) GYROSIGMA-BALTICUM (EHRENBERG) RABENHORST, GYROSIGMA-PENSACOLAE SP-N AND SIMULACRUM SPECIES

'Simulacrum species' have been hidden within the current concept of Gy rosigma balticum (Ehrenberg) Rabenhorst because the traditional taxono mic criteria did not permit their recognition. Thus, records of this c ommon species may actually relate to a different organism. A neotype o f Gyrosigma balticum is designated and a revised and extended species description is given. Two simulacra are discussed: Gyrosigma pensacola e n. sp. and a species referred to as 'Gyrosigma non-balticum'. This m ust be conspecific with G. sterrenburgii Stidolph and raises questions regarding its distribution.