Gymnodinium cyaneum Hu was described in 1980 on the basis of materials collectedfrom fishponds in Wuchang,Hubei Province(Hu et al,1980).The name is,however,illegitimatized by the earlier homonym G.eyaneum Schiller(1955);moreover,no Latindiagnosis was provided.It is therefore necessary to republish the species under the newname G.eucyaneum with the following Latin diagnosis: Gymnodinium cyaneum Hu was described in 1980 on the basis of materials collected from fishponds in Wuchang, Hubei Province (Hu et al, 1980). The name is, however, illegitimatized by the earlier homonym G.eyaneum Schiller (1955); moreover, no Latindiagnosis was provided. It is therefore necessary to republish the species under the newname G.eu cyaneum with the following Latin diagnosis: