Eight novel pfiesteria-similar dinoflagellates are described that form a genetically well-defined group with distinct morphological features, and are capable of feeding myzocytotically on cryptophytes and other algae. Taxonomically, there was concordance between the genetic analysis and plate tabulation features among these taxa. It is suggested that these dinoflagellates are important grazers of other phytoplankton in the environment, and their total ecological significance has been underestimated.