Dianoflagellates

• Mostly marine and photosynthetic.
• They appear yellow, green, brown, blue or red depending on the main pigments present in their cells.
• The cell wall has stiff cellulose plates on the outer surface.
• Most of them have 2 flagella; one lies longitudinally and the other transversely in a furrow between the wall plates.
• Red dianoflagellates (E.g. Gonyaulax) undergo rapid multiplication so that the sea appears red (red tides).
• Toxins released by such large numbers can kill other marine animals such as fishes.