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.