any of the approximately 20 species of wood-boring, marine crustaceans constituting the genus Limnoria, in the order Isopoda. They feed on algae, driftwood, and the submerged wood of docks and wharves and sometimes attack the nonwoody insulation of submarine cables.

Limnoria lignorum, which occurs throughout the seas of the Northern Hemisphere, grows to 5 mm (0.2 inch) in length and has a gray body consisting of 14 clearly defined segments. It burrows about 12 mm into wood. L. tripunctata occurs in the Atlantic Ocean from New England (U.S.) to Venezuela and in the Pacific Ocean from California to Mexico. It even penetrates wood that has been impregnated with creosote, an offensive chemical that repels most wood-boring invertebrates. L. pfefferi is found in the Pacific and Indian oceans; L. saseboensis is found on the Atlantic coast of the southeastern United States and on the coast of Japan.