Fragilidium fissile Balech (Dinophyceae): Life-history, morphology, phylogenetic position and feeding activity

Abstract

IntroductionThe 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. Owen and Norris (1985) described the resting cyst of Fragilidium sp., and suggested this species has a similar life history with other dinoflagellates, such as Alexandrium species. Nevertheless, a detailed description has not been observed of resting cyst germination, in which single cells are followed through the process, nor has there been a rigorous study of life stages transitions, two aspects of great importance. 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.Results and DiscussionFragilidium-like resting cysts characterized by transparent and round shape were isolated from sediment trap samples of Masan Bay, Korea. 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 thecate planozygotes were larger than vegetative cells. The vegetative cell was identified as Fragilidium fissile on the basis of theca morphology and tabulation the plat and Norris (1985) described the resting cyst of Fragilidium sp., and suggested this species has a similar life history with other dinoflagellates, such as Alexandrium species. Nevertheless, a detailed description has not been observed of resting cyst germination, in which single cells are followed through the process, nor has there been a rigorous study of life stages transitions, two aspects of great importance. 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.Results and DiscussionFragilidium-like resting cysts characterized by transparent and round shape were isolated from sediment trap samples of Masan Bay, Korea. 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 thecate planozygotes were larger than vegetative cells. The vegetative cell was identified as Fragilidium fissile on the basis of theca morphology and tabulation the plat