Dinoflagellates are unicellular protists which exhibit a great diversity of form. The largest, Noctiluca, may be as large as 2 mm in diameter! Though not large by human standards, these creatures often have a big impact on the environment around them. Many are photosynthetic, manufacturing their own food using the energy from sunlight, and providing a food source for other organisms. Some species are capable of producing their own light through bioluminescence, which also makes fireflies glow. There are some dinoflagellates which are parasites on fish or on other protists.
The most dramatic effect of dinoflagellates on life around them comes from the coastal marine species which "bloom" during the warm months of summer. These species reproduce in such great numbers that the water may appear golden or red, producing a "red tide". When this happens many kinds of marine life suffer, for the dinoflagellates produce a neurotoxin which affects muscle function in susceptible organisms. Humans may also be affected by eating fish or shellfish containing the toxins. The resulting diseases include ciguatera (from eating affected fish) and paralytic shellfish poisoning, or PSP (from eating affected shellfish, such as clams, mussels, and oysters); they can be serious but are not usually fatal.
For additional information:
For an excellent summary of modern dinoflagellates, click here for Andrew MacRae's Dinoflagellates page at the University of Calgary. You can also try the Protist Image Data Base for information about the dinoflagellate genus Peridinium. Or read Jeff Shield's page on Parasitic dinoflagellates of crustaceans.
For a fuller listing of on-line phycological collections resources, try our Phycological Collections Catalogs Listings.
You can get information about ciguatera fish poisoning and shellfish poisoning from the Food and Drug Administration's on-line handbook of foodborne pathogenic microbes and natural toxins.
Handbook of Protoctista by L. Margulis et al., 1990 Jones and Bartlett, chapter on Dinoflagellata by F. J. R. Taylor