Bitectatodinium tepikiense Wilson cysts, first described from Pleistocene sediments and generally associated with sediments in temperate to cold-temperate waters, were germinated to establish cultures. The motile thecate cells derived were referable to Gonyaulax digitale (Pouchet) Kofoid. For the first time detailed morphological information is given for the motile stage of this cyst–theca relationship. Cultures were re-encysted; the cultured cysts showed a range of morphology from spherical cysts to those with an apical boss. The taxonomy of Gonyaulax digitale and cyst–theca relationships within the Spiniferites plexus are discussed but, given the debate surrounding the status of the genera Gonyaulax and Spiniferites, no formal taxonomic reassignments are proposed. These observations confirm that establishing cultures of cyst taxa in problematic dinoflagellate groupings and meticulous high-resolution scanning electron microscopic observation of the specimens have great potential for elucidating cyst–theca relationships and clarifying dinoflagellate taxonomy.
