Morfology and taxonomy of several species of the diatomean genus Coscinodiscus from the Mexican Pacific coast

Net phytoplankton samples (30 mu m and 54 mu m mesh), from coasts of the Pacific Ocean of Mexico, including coasts of Baja California, the Gulf of California and Tehuantepec (1982-1986); were analyzed to provide a revision of species of the diatom genus Coscinodiscus. Six species were found and studied by light;and electron microscopy. Typical references, morphological details, and a brief discussion on morphological variability and taxonomic aspects are given for each species, as well as the local and general distribution. Coscinodiscus radiatus appeared as the most widespread species, perhaps because some taxa have become minor synonyms of it. The valuable taxonomic characteristics of the genus Coscinodiscus are: form of the valve, presence of valve process, relative height of mantle, other specific characteristics.