The Prorocentrum cordatum/Prorocentrum minimum taxonomic problem

For more than 80 years there have existed two species Prorocentrum cordatum (Ostenfeld) Dodge (= Exuvianella cordata Ostenfeld. 1901. originally ident ified in Caspian Sea samples), and Prorocentrum minimum (Pavillard) Schille r (= Exuviaella minima Pavillard, 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. minimum is found in different water basins and many authors have increasingly repo rted frequent blooms of this species during the last decades (Smayda 1990, Hallegraeff 1993). Until the end of the 1960-s P. cordatum was considered e ndemic and prominent in the Caspian. Black, Azov and Aral Seas. The first SEM examination of the Black Sea P. cordatum indicated misidentif ication. There was a proposal for its renaming into P. minimum. which had n ever been reported from the Black Sea before. There has been no general agr eement on this and the necessity to re-examine samples both from the Black and Caspian Seas has become evident. The present study of the original Caspian P. cordatum and the suspicious Bl ack Sea species shows the con-specificity of P. minimum and P. cordatum. Th e missing detail, namely the invisible apical spine, is round in all P. cor datum specimens. We propose P. minimum as a synonym of P. cordatum.