Perkinsus marinus is a protistan parasite that infects the Eastern Oyster, Crassostrea virginica, and is one factor responsible for the reduced productivity of oyster fisheries. This parasite (or related species) has a wide distribution and has also been found to infect the oysters in the Tampa Bay region. A significant aspect of this organism has been its enigmatic taxonomic position. Originally classified in two separate fungal genera, it currently is considered an Apicomplexan (Kingdom Protista) based on transmission electron microscopy studies of the zoospore revealing an apical complex. However, rRNA studies have shown that P. marinus may be more closely related to the dinoflagellates. The focus of my study has been on surface features of certain developmental stages that may aid in a definitive taxonomic placement of this organism.

Transmission electron microscopy observations of the trophozoite and hypnospore stages show variation in both the size of the organism and the presence of a cell wall.