The mussel is a bivalve (hinged shell) mollusc of either the marine order Mytiloida or the freshwater superfamily Unionacea. Mussels, prized worldwide for food, are the moule of French cuisine. Marine mussels are elongated by enlargement of the posterior end. They are found attached to a support by byssal threads (filaments secreted by the mollusc) or partially buried. The blue, bay or common mussel (Mytilus edulis) occurs on Canada's East and West coasts and is the only mussel of commercial interest in this country. Recent aquaculture operations in the Maritimes have been successful. In 1996, 9832 t were produced on the Atlantic coast. Two other mussels provide a recreational fishery and have potential for development: sea mussels (M. californianus), found on the exposed West Coast, and horse mussels (Modiolus modiolus), present in deeper waters of the Pacific and Atlantic coasts. In late 1987 a ban on East Coast mussels was the result of some 100 people becoming ill and at least 2 dying from eating Maritime mussels. The demoic acid toxin was responsible.