medical Definition of Dinoflagellata
: a division or phylum of chiefly marine unicellular plantlike protists that comprise the dinoflagellates, that are typically enclosed in a cellulose envelope, that have one transverse flagellum running in a groove about the body and one posterior flagellum extending out from a similar median groove, and that include luminescent forms, important elements of marine food chains, and most of the the flagellates that cause red tide (such as members of the genus Gymnodinium)
