Mussels present the greatest hazard for shellfish poisoning, but clams, oysters, and scallops also concentrate the toxins. Crab and shrimp do not feed on the toxic dinoflagellates and pose no danger of shellfish poisoning. Approximately 20 of 1200 dinoflagellata species produce toxins which cause significant illness in human body. Around 20 toxins, produced by dinofilagellates, are known. Four toxic syndromes have been caused to ingestion of shellfish. There are paralytic, neurotoxic, diarrhetic, and amnesic shellfish poisoning.