3 NEW SPECIES OF THE GENUS ALEXANDRIUM (DINOFLAGELLATA)

Three new species of the dinoflagellate genus Alexandrium are describe d. Alexandrium tamiyavanichi is in the subgenus Alexandrium in which t he Po and 1' are connected. This species is closely related to A. coho rticula, 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 specie s belong in the subgenus Gessnerium in which the Po and 1' are complet ely disconnected. Alexandrium taylori has a pentagonal 1' and a ventra l 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 o f this genus described to date with a quadrangular 1'; it also has a v entral pore. Of the three species, only A. tamiyavanichi is known to p roduce paralyzing shellfish poisoning