A gribble is any species of marine isopods from the family Limnoriidae. They are mostly pale white and small crustaceans resembling an ordinary wood louse, 6 mm in length with 7 pairs of
legs and 4 pairs of mouthparts. Limnoriidae have various species which bore into marine plants as well as submerged intact wood or timber.There are three known genera, Paralimnoria, Limnoria, and Lynseia. Limnoria has species present in most seas around the world.
Gribbles bore into wood and plant material for food. .The term gribble was originally used for the wood-boring species, Limnoria lignorum. The most destructive species are Limnoria lignorum, L. tripunctata and L. quadripunctata.
Gribbles are able to make an enzyme cellulase to dissolve cellulose present in plant cell walls. Other animals like termites that feed on plant fibres make use of other microorganism in their gut to produce cellulase.
Image of gribble, Limnoria, a crustacean showing ventral view with eggs.
Image from http://simple.wikipedia.org/wiki/File:Limnoria_eggs.jpg