Most persons concerned with problems of marine corrosion are acquainted with the importance of the shipworm and the ravages of the gribble, Limnoria. Both are marine wood borers whose combined activities have been estimated to cause $50 million damage annually in the United States (2). Shipworms occasionally have been responsible for spectacular economic losses, such as the extensive dock failures in San Francisco Bay between 1917 and 1919 (1), and the more recent collapse of a bridge in New Jersey (3). Instances such as those mentioned have kept our interest in the prevention and control of wood borers at a high level. Corrosion caused by other large organisms on other materials has naturally occupied little attention. However, the recent destruction of steel piling by sea urchins along the Pacific coast indicates that a review of the modus operandus of the various known categories of marine borers could serve the useful purpose of preparing ourselves for any future costly attacks.