Shipworm, or Teredo, name for a family of shelled marine animals. Although they resemble worms, shipworms are mollusks. A shipworm has along slender body and a small two-part shell attached to the anterior (front) end of the body. The body is very long in relation to the shell; for example, one species commonly found in North American waters can grow up to two feet (60 cm) long, but its shell is only one-half inch (13 mm) long. There are more than 65 shipworm species, ranging in length from 10 inches (25 cm) to more than three feet {90 cm). Shipworms are found in all but polar seas.

The small shells function as boring tools that shipworms use to burrow into submerged wood, such as in wharf piles and boats. Once they attach themselves to a wooden structure, they burrow deeper and deeper. They can eventually so weaken the wood that it breaks apart. The wood is the main food source for shipworms.

Shipworms make up the family Teredinidae.