Heterocapsa circularisquama is a species of Dinoflagellate notable for the production of a biotoxin affecting marine fauna. It is known to produce large red tides off western Japan, causing high bivalve mortality, particularly pearl oysters. It is very similar to Heterocapsa illdefina, however H. circularisquama carries six radiating ridges on its circular basal plate, and its scales have longer spines, among other subtle differences in morphology.