Hidden infections in dinoflagellate hosts

Free-living core dinoflagellates are commonly infected by members of two parasitic clades that are themselves closely related to dinoflagellates, the syndinians and perkinsids. These parasites are abundant and ecologically important, but also difficult to observe directly or cultivate, so our knowledge of them is usually restricted to environmental 18S rDNA sequences, and genome-scale molecular data are not available for most species. Here, we report numerous syndinian parasites and one parasite that is sister to all known perkinsids from isolated single cells of diverse, free-living dinoflagellates.