Comparative study ofGymnodinium mikimotoiandGymnodinium aureolum, comb. nov. (=Gyrodinium aureolum) based on morphology, pigment composition, and molecular data

Light and electron microscopy, nuclear‐encoded LSU rDNA sequences, and pigment analyses were performed on five geographically separate isolates ofGymnodinium mikimotoi.The morphological variation between the isolates equals that found within the isolates. The nuclear‐encoded LSU rDNA sequences were nearly identical in all isolates, and molecular analyses using maximum likelihood, parsimony, and neighbor joining showed the geographical isolates as an unresolved clade. Based on the available data it is concluded that the European isolates, formerly identified asGyrodinium aureolum,Gyrodiniumcf.aureolum, orGymnodiniumcf.nagasakiense, are conspecific with the JapaneseGymnodinium mikimotoi.An isolate from the Pettaquamscutt River, USA, is suggested to represent what Hulburt (1957) described asGyrodinium aureolum.The LSU rDNA sequence data and ultrastructural characters in this isolate closely resemble those ofGymnodinium fuscum, the type species ofGymnodinium, andGyrodinium aureolumHulburt is therefore renamedGymnodinium aureolum(Hulburt) G. Hansen, comb. nov.