Location: Bi-valve shellfish, such as mussels, clams, oysters, scallops, cockles, and other shellfish that naturally have two hinged shells thrive in many US marine locations such as New England, the Pacific Coast, and Alaska, as well as the Mexican and Canadian coasts. They can become poisonous during warm seasons when they feed on certain dinoflagellates, microscopic cellular beings, as Gony-aulax catenella, which carry potent nerve poisons.

Effects and Symptoms: A nitrogenous compound in the shellfish produces curarelike muscular paralysis. After ingesting infested bi-valves, numbness, tingling of lips, tongue, face, and extremities can occur; followed by nausea, vomiting and sometimes even convulsions. Symptoms can often progress to respiratory paralysis and death. The symptoms start within a half hour of ingestion. Recovery is likely if the victim survives the first twelve hours. Fatalities occur in approximately ten percent of all cases.

Government agencies sometimes issue warnings advising people not to eat particular shellfish during certain times of the year. The mortality rate of those consuming toxic shellfish is sometimes quite high, with mussels producing the highest death rate of all the bivalve shellfish.