Comparative study of Gymnodinium mikimotoi and Gymnodinium aureolum, comb.nov (= Gyrodinium aureolum) based on morphology, pigment composition, and molecular data

Light and electron microscopy, nuclear-encoded LSU rDNA sequences, and pigm ent analyses were performed on five geographically separate isolates of Gym nodinium mikimotoi, The morphological variation between the isolates equals that found within the isolates. The nuclear-encoded LSU rDNA sequences wer e nearly identical in all isolates, and molecular analyses using maximum li kelihood, parsimony, and neighbor joining showed the geographical isolates as an unresolved clade. Based on the available data it is concluded that th e European isolates, formerly identified as Gyrodinium aureolum, Gyrodinium cf. aureolum, or Gymnodinium cf. nagasakiense, are conspecific with the Ja panese Gymnodinium mikimotoi. An isolate from the Pettaquamscutt River, USA , is suggested to represent what Hulburt (1957) described as Gyrodinium aur eolum. The LSU rDNA sequence data and ultrastructural characters in this is olate closely resemble those of Gymnodinium, and Gyrodinium, the type speci es of Gymnodinium, and Gyrodinium aureolum Hulburt is therefore renamed Gym nodinium aureolum (Hulburt) G. Hansen, comb. nov.