Pteriatoxins A, B and C, extremely potent toxins, were isolated from the Okinawan bivalve Pteria penguin. Their structures were determined based on NMR and MS/MS spectral analyses. Pteriatoxins have polyether macrocycles composed of 6,7-spiro, 5,6-bicyclo and 6,5,6-trispiro ketal rings, the same as in pinnatoxins.