Fine structural observations on Gonyaulax spinifera (Dinophyceae), with special emphasis on the flagellar apparatus

The fine structure of Gonyaulax spinifera (Claparede et Lachmann) Diesing has been investigated by transmission electron microscopy, using serial sections. The cell has a single multilobed chloroplast and a central pyrenoid complex; a common plastidial origin for gonyaulacoid dinoflagellates is indicated. The cell contains an apical fibrous pore complex, comprising numerous striated fibres that radiate from the apical pore region. The fibres do not seem to originate from a fibrous ring or disc as observed in other dinoflagellates. The pusular system consists of two large sacs, and numerous tubules connect with the sacs. One sac opens into the transverse, the other into the longitudinal flagellar canal. Each flagellar canal is surrounded by a prominent striated collar. The collars are interconnected by a broad striated fibre and an accessory striated fibre not observed in other dinoflagellates. The basal bodies are almost antiparallel (i.e. of opposite polarity), a feature hitherto observed only in some naked species. The flagellar apparatus (FA) comprises the components usually associated with dinoflagellates: the longitudinal microtubular root, the transverse striated root, and the transverse striated root microtubule. The most significant difference between the FA of the gonyaulacoids Ceratium hirundinella var. furcoides (Schroder) Huber-Pestalozzi and G. spinifera is the presence, in Ceratium, of a dorsal fibrous component and a ventral striated component. A microtubular strand, similar in appearance and location to the feeding apparatus of hetero- and mixotrophic dinoflagellates, is present in G. spinifera indicating potential mixotrophic behaviour.