Shipworms are not in fact worms at all, but rather a peculiar variety of marine mollusk (Eulamellibranchiata). They bore into submerged wood and are one of the few animals capable of digesting cellulose directly. The shipworms belong to several genera of which Teredo is the most commonly mentioned.
Shipworms have slender worm-like forms, but possess the characteristic structures of bivalves. The valves of the shell are small separate parts located at the anterior end of the worm, used for excavating the burrow. Shipworms do great amounts of damage to wooden hulls and marine piling, and have been the subject of much study to find methods to avoid their attacks.