Limnoria lignorum, commonly known as the gribble, is a species of isopod in the family Limnoriidae. It is found in shallow water in the North Atlantic and North Pacific Ocean where it tunnels into wood and attacks and destroys submerged wooden structures.

Isopoda is an order of crustacean, which includes woodlice and their relatives. Members of this group are called Isopods and include both terrestrial and aquatic species. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and five pairs of branching appendages on the abdomen that are used in respiration. Females brood their young in a pouch under their thorax.