HERMAPHRODITES. “By contrast, hermaphroditism is rare among animals considered as a whole (about 5% of all species), which is largely due to the absence of hermaphrodites in the species-rich insects, but it is common in many other animal taxa, including fish and many invertebrates (most snails, corals, trematodes, barnacles, and many echinoderms).”
http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001899