genus of dinoflagellates (single-celled aquatic organisms) that inhabit fresh, salt, or brackish water. Members are .... plankton form,

Members are covered by closely fitting cellulose plates and have two flagella: one extends downward from a longitudinal groove in the armour, and the other, in an encircling groove, appears to keep the animal afloat. polyedra, a toxic planktonic form, is sometimes abundant enough to colour water and cause the phenomenon called ( q.v. plankton form,