Gymnodinium

noun

Gym·​no·​din·​i·​um ˌjim-nə-ˈdin-ē-əm 

: a large genus (the type of the family Gymnodiniidae) of marine and freshwater naked dinoflagellates that includes forms which are colorless or tinted yellowish to reddish brown, blue, or green by chromatophores and a few forms which cause red tide