Any long, slender, worm-shaped bivalve mollusk of Teredo and allied genera. The shipworms burrow in wood, and are destructive to wooden ships, piles of wharves, etc. See Teredo.

wormlike marine bivalve that bores into wooden piers and ships by means of drill-like shells

Shipworms are not in fact worms at all, but rather a group of marine mollusk (Eulamellibranchiata) in the family Teredinidae. They bore into submerged wood, and bacteria in a special organ called the gland of Deshayes enable them to digest cellulose. The shipworms belong to several genera of which Teredo is the most commonly mentioned.