Three 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 For the past several years, I have worked on a revision of the dinoflagellate genus Alexandrium Halim, 1960, which is of great practical importance because several of its members are associated with human poisoning caused by ingestion of toxic seafood. This taxonomic revision, which is in final preparation, is based on examination of numerous specimens collected world-wide from most of the geographic locations from which members of the genus have been recorded. However, to provide more immediate knowledge of three new species, descriptions are presented earlier here. MATERIALS AND METHODS Material for Alexandrium tamiyavanichi came from a culture initiated from a specimen obtained at Ang Sila in the Gulf of Thailand. Material for Alexandrium taylori came from a plankton sample collected in the bay of Arcachon, France. Specimens of A. margalefi came from plankton samples and from cultures, both from Vigo, Spain. Specimens of each of the three species were isolated, drawn, and measured. Many thecae were dissociated with the aid of sodium hypochlorite, which destroyed the protoplasm and separated the plates so that they were distinguishable. Plates were studied with a light microscope using bright-field oil immersion and phase-contrast objectives. ' I thank Dr. T. Piyakarnchana and Miss Sucharno for the material from Thailand, Dr. P. Lassus for the samples from Arcachon and the Bay of Douarnenez, France, and Drs. J. Blanco and S. Fraga for the plankton samples and cultures from Vigo, Spain. I specially thank Dr. K. A. Steidinger and Miss B. S. Roberts for suggestions, criticisms, and help with the manuscript. TRANS. AM. MICROSC. SOC., 113(2): 216-220. 1994. ? Copyright, 1994, by the American Microscopical Society, Inc. This content downloaded from 207.46.13.16 on Thu, 16 Jun 2016 06:13:47 UTC All use subject to http://about.jstor.org/terms VOL. 113, NO. 2, APRIL 1994