A few species of algae produce neurotoxins. For example , some genera of dinoflagellates,such as Alexandrium, are important medically because they produce a nenrotoxin called saxitoxin. Although mollusks that feed on the dinoflagellates that produce saxitoxin show no symptoms of disease,people who eat the mollusks develop paralytic shellfish poisoning, with symptoms similar to botulism. Public health agencies frequently prohibit human consumption of mollusks during red tides