For more than 80 years there have existed two speciesProrocentrum cordatum(Ostenfeld) Dodge (=Exuviaella cordataOstenfeld, 1901, originally identified in Caspian Sea samples), andProrocentrum minimum(Pavillard) Schiller(=Exuviaella minimaPavillard, 1916, the Gulf of Lion). Morphologically they differ only by the apparent complete absence of an apical spine in P.cordatum.Their environmental preferences are also very similar. P.minimumis found in different water basins and many authors have increasingly reported frequent blooms of this species during the last decades (Smayda 1990, Hallegraeff 1993). Until the end of the 1960-sP. cordatumwas considered endemic and prominent in the Caspian, Black, Azov and Aral Seas.