Fragilidinium fissile (Dinophyceae): Life history, morphology and phylogenetic position

Abstract

The mixotrophic dinoflagellate Fragilidium Balech has been reported rarely in taxonomic checklists, probably as a consequence of its confusion with the genus Alexandrium, and also the biological features are poorly known. In this study, we investigated the life history of mixotrophic dinoflagellate Fragilidium observed from Masan Bay, Korea and clarified the morphology and phylogenetic position using partial large subunit ribosomal DNA gene sequences. Fragilidium-like resting cysts characterized by transparent and round shape were isolated from sediment trap samples of Masan Bay, Korea, and we were able to observe the processes of germination. The isolated resting cysts germinated into gymnodinoid planozygote and directly formed the pellicle cyst, and then the thecate planozygote was observed after the germination of pellicle cyst. The gymnodinoid and planozygotes are larger than vegetative cells. Vegetative cell was identified as Fragilidium fissile on the basis of theca morphology and tabulation the plate formula is Po, Pc, 4’, 8’’, 10c, 6s?, 7’’’,2’’’’, 1p. Comparisons of partial large subunit ribosomal DNA gene sequences reveal that F. fissile is allied with, but distinct from the other Fragilidium species.investigated the life history of mixotrophic dinoflagellate Fragilidium observed from Masan Bay, Korea and clarified the morphology and phylogenetic position using partial large subunit ribosomal DNA gene sequences. Fragilidium-like resting cysts characterized by transparent and round shape were isolated from sediment trap samples of Masan Bay, Korea, and we were able to observe the processes of germination. The isolated resting cysts germinated into gymnodinoid planozygote and directly formed the pellicle cyst, and then the thecate planozygote was observed after the germination of pellicle cyst. The gymnodinoid and planozygotes are larger than vegetative cells. Vegetative cell was identified as Fragilidium fissile on the basis of theca morphology and tabulation the plate formula is Po, Pc, 4’, 8’’, 10c, 6s?, 7’’’,2’’’’, 1p. Comparisons of partial large subunit ribosomal DNA gene sequences reveal that F. fissile is allied with, but distinct from the other Fragilidium species.