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We investigate the cyst-theca relationship of Impagidinium caspienense. Through an incubation experiment, we succeeded in examining the motile stage. Additional molecular analysis of single-cyst PCR (LSU and SSU rDNA) reveal that the cyst is related to the species Gonyaulax baltica Ellegaard et al. (). The ability of this species to belong to two types of cyst-based genera (spiniferate and impagidinioid) suggests that environmental (particularly salinity) and not genetic factors explain the formation of both morphotypes by G. baltica, which provides evidence for heterospory in this species. The affiliation to G. baltica demonstrates that I. caspienense is not endemic to the Caspian Sea. The phylogenetic position of several other gonyaulacoid species is also documented: Impagidinium pallidum, Ataxiodinium choane, Pyxidinopsis psilata, Spiniferites belerius, and Spiniferites ramosus. The LSU and SSU rDNA based phylogenies suggest that the genera Impagidinium and Spiniferites are not monophyletic, and that P. psilata and A. choane are close to Gonyaulax verior and Gonyaulax polygramma, respectively. In addition, this study accentuates the importance of cyst morphology in the classification of the Gonyaulacales., (© 2017 The Author(s) Journal of Eukaryotic Microbiology © 2017 International Society of Protistologists.)

The cyst-theca relationship of Protoperidinium fukuyoi n. sp. (Dinoflagellata, Protoperidiniaceae) is established by incubating resting cysts from estuarine sediments off southern Vancouver Island, British Columbia, Canada, and San Pedro Harbor, California, USA. The cysts have a brown-coloured wall, and are characterized by a saphopylic archeopyle comprising three apical plates, the apical pore plate and canal plate; and acuminate processes typically arranged in linear clusters. We elucidate the phylogenetic relationship of P. fukuyoi through large and small subunit (LSU and SSU) rDNA sequences, and also report the SSU of the cyst-defined species Islandinium minutum (Harland & Reid) Head et al. 2001. Molecular phylogenetic analysis by SSU rDNA shows that both species are closely related to Protoperidinium americanum (Gran & Braarud 1935) Balech 1974. Large subunit rDNA phylogeny also supports a close relationship between P. fukuyoi and P. americanum. Three subgroups in total are further characterized within the Monovela group. The cyst of P. fukuyoi shows a wide geographical range along the coastal tropical to temperate areas of the North-east Pacific, its distribution reflecting optimal summer sea-surface temperatures of ~14-18 °C and salinities of 22-34 psu., (© 2013 The Author(s) Journal of Eukaryotic Microbiology © 2013 International Society of Protistologists.)