3 NEW SPECIES OF THE GENUS ALEXANDRIUM (DINOFLAGELLATA)

Three new species of the dinoflagellate genus Alexandrium are described. Alexandrium tamiyavanichi is in the subgenus Alexandrium in which the Po and 1' are connected. This species is closely related to A. cohorticula, but it differs by its general shape, the Po and 1', the shape of its left sulcal list, and some sulcal plates. The other two species belong in the subgenus Gessnerium in which the Po and 1' are completely disconnected. Alexandrium taylori has a pentagonal 1' and a ventral pore. It differs from the closely related species A. pseudogoniaulax (Biecheler) by the shape of 1', the position of the ventral pore, and all of the sulcal plates. Alexandrium margalefi is the only species of this genus described to date with a quadrangular 1'; it also has a ventral pore. Of the three species, only A. tamiyavanichi is known to produce paralyzing shellfish poisoning