On the Identity and Taxonomic Circumscription of the Pfiesteriacean Genera Aduncodinium and Speroidium (Dinophyceae)

With its former circumscription, the genus Katodinium included purportedly naked species with a much larger epi- than hypocone, several of which were shown to be distantly related to the type species K. nieuportense. Most of these species have recently been transferred to other genera, several of them newly established. Among these new genera, Aduncodinium was proposed to encompass Katodinium glandula (=Gymnodinium glandula), and Speroidium was erected to encompass Katodinium fungiforme (=Gymnodinium fungiforme). However, the genus Aduncodinium was invalidly published and several morphological aspects described need to be re-evaluated. On the other hand, the inclusion in K. fungiforme of morphological and molecular characters observed in the strain known as VDH034S “Bullet,” a pfiesteriacean, needs re-evaluation because the latter shows a higher resemblance to Aduncodinium species than to K. fungiforme. The present contribution aimed to clarify the identity of the taxa involved on the basis of newly collected morphological and molecular information, and thereby avoid the nomenclatural and taxonomical uncertainties raised by previously published concepts of the genera Aduncodinium and Speroidium.