TERE'DO, a genus of lamellibranchiate mollusks of the family pholadidce; very much elongated, and worm-shaped; the mouth very delicate, open in front and at its lower part, for the passage of the short foot; the shell rather thick, equivalve, destitute of hinge, gaping at both ends. The species are rather numerous, and are generally known by the name of SHIPWORNI or PILEWOILM, because they perforate and live in timber. Their perforations are made in the direction of the grain of the timber, except when a knot is met with or the shell of another teredo, when they accommodate themselves to circumstances by bending. The cavity is lined with a calcareous incrustation. The aperture by which the teredo enters is small, and it grows Within the cavity which it makes. Two small valves form the true bivalve shell ; the calcareous tube incloses the worm-shaped body of the animal. Its growth is very rapid, and its ravages are often
terrible. A piece of deal has been found riddled by shipworms after forty days' immer sion. Ships, piles, and all submarine woodwork are destroyed by it. Copper-sheathing is employed to protect ships from the shipworm, or the timber is driven full of short, broad-headed nails, the rusting of which forms a coating which it does not penetrate. The dykes of Holland have been threatened with destruction by its ravages. The Com 2,rox SHIPWORM (teredo navalis) is said to have been introduced into Europe from warmer climates. It is now, however, extremely abundant in European seas. In the East Indies, a very large species (teredo gigantea) is found, generally in shallow water among mangrove trees; it is sometimes more than five feet in length, and at the thickest part three inches in diameter.