Based on samples obtained in 20002002 from a 1cm layer of surface sediment at two sites in Bahía Concepción in the Gulf of California, cysttheca relationships were defined from cyst germination assays for Gonyaulax spinifera (= Spiniferites mirabilis), Protoceratium globosum, Preperidinium meunieri (= Dubridinium caperatum), Protoperidinium denticulatum (= Brigantedinium irregulare), and Protoperidinium cf. thorianum. All the taxa are illustrated with photomicrographs and descriptions of the resting and vegetative stages are given, including synonymy, size variation, distribution in Mexico, and global distribution, when known. As a result of cyst germination assays, the previously unknown cysttheca relationship of P. globosum was described. We also confirmed the presence of the vegetative stage of P. denticulatum in the Gulf of California and heterospory in G. spinifera from Bahía Concepción. Cultures of G. spinifera and P. globosum were successfully established.
