It is commonly reported that at least 50% of the world species are parasites because almost all free-living organisms are host of one or more parasitic taxa. The parasitism is one of the black boxes of the marine ecosystems. Parasitism causes mortalities in fisheries and aquaculture, and the parasites may constitute a tool for the biological control of the harmful bloomsand/or invasive species. Nearly all the basal dinoflagellates and ~90 species of core dinoflagellates are parasites able to infect a broad array of protist and animal hosts. We examine the parasites of the copepods, the most abundant animal group on Earth. We report the morphology, life cycle and molecular phylogeny of the copepod endoparasitesBlastodiniumandSyndinium, the ectoparasiteEllobiopsis, and the egg-infestingDissodiniumandChytriodinium. We alsoexamineOodiniumandApodinium, ectoparasites of appendicularians (Appendicularia, gelatinous plankton);AmyloodiniumandIchthyodinium, parasites of fishes; andAmoebophryaandEuduboscquellaas endoparasites of dinoflagellates and ciliates, respectively.
