Hematodinium is a genus of dinoflagellates. Species in this genus, such as Hematodinium perezi, the type species, are internal parasites of the hemolymph of crustaceans such as the Atlantic blue crab (Callinectes sapidus) and Norway lobster (Nephrops norvegicus). Species in the genus are economically damaging to commercial crab fisheries, including causing bitter crab disease in the large Tanner or snow crab fisheries of the Bering Sea.