Five Karenia species along the Chinese coast: With the description of a new species, Karenia hui sp. nov. (Kareniaceae, Dinophyta)

•Novelty: five Karenia species, K. longicanalis, K. papilionacea, K. mikimotoi, K. selliformis, and a new species, Karenia hui sp. nov., were isolated from Chinese coastal waters.•Methodology: morphological features, ultrastructure characters, photosynthetic pigments, the large subunit (LSU) of the rRNA gene, the internal transcribed spacer (ITS) sequences, acute toxicity analysis and gymnodimines (GYMs) contents of the karenia species were analyzed.•Results: 1) a new species, karenia hui sp. nov., was identified. 2) the five karenia species are toxic to marine medakas. 2) four karenia species, K. longicanalis, K. papilionacea, K. mikimotoi and K. selliformis are capable of producing the toxin GYM-A.•Contribution to the Field: karenia mikimotoi blooms in china are usually a mixture of Karenia spp. or other Kareniaceans. Karenia species, notably K. selliformis, emerge as potential sources of GYMs in shellfish in China. Dinoflagellates within the genus Karenia are well known for their potential to cause harmful algal blooms and induce detrimental ecological consequences. In this study, five Karenia species, Karenia longicanalis, Karenia papilionacea, Karenia mikimotoi, Karenia selliformis, and a new species, Karenia hui sp. nov., were isolated from Chinese coastal waters. The new species exhibits the typical characteristics of the genus Karenia, including a linear apical groove and butanoyl-oxyfucoxanthin as the major accessory pigment. It is distinguished from the other Karenia species by a wide-open sulcal intrusion onto the epicone, a conical epicone with an apical crest formed by the rim of the apical groove, and a hunchbacked hypocone. It is most closely related to Karenia cristata, with a genetic divergence of 3.16 % (22 bp out of 883 bp of LSU rDNA). Acute toxicity tests indicated that the five Karenia species from China are all toxic to marine medaka Oryzias melastigma. Karenia selliformis and K. hui were very toxic to O. melastigma, resulting in 100 % mortality within 4 h and 24 h, respectively. Further analysis by high-performance liquid chromatography revealed that four species, K. selliformis, K. longicanalis, K. papilionacea and K. mikimotoi were capable of producing Gymnodimine-A (GYM-A). The highest GYM-A content was in K. selliformis (strain HK-43), in which the value was 889 fg/cell. No GYM-A was detected in the new species K. hui, however and its toxin remains unknown. Below we provide a comprehensive report of the morphology, phylogeny, pi