The shipworms, also called Teredo worms or simply Teredo, are marine bivalve molluscs in the family Teredinidae, a group of saltwater clams with long, soft, naked bodies. They are notorious for boring into wood that is immersed in seawater, including such structures as wooden piers, docks, and ships; they drill passages by means of a pair of very small shells ("valves") borne at one end, with which they rasp their way through. They are sometimes called "termites of the sea". Carl Linnaeus assigned the common name Teredo to the best-known genus of shipworms in the 10th edition of his taxonomic magnum opus, Systema Naturæ (1758).
Shipworm
Teredo navalis from Popular Science Monthly, September 1878
Disposition of the main organs in a shipworm. GDA: anterior digestive gland; GDV: ventral digestive gland, with its orifices in the stomach. Orifices uri. et gen., urinary and gential orifices. The left ventricle is sectioned near its base. The nerve ganglion is in blue. The distance between pallets and foot spans several time the animal's diameter.
Teredolites borings in a modern wharf piling. The US one cent coin in the lower left of this image is 19 mm across.
Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bivalves have no head and they lack some usual molluscan organs, like the radula and the odontophore. The class includes the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment, where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. Shipworms bore into wood, clay, or stone and live inside these substances.
Bivalvia
Empty shell of the giant clam (Tridacna gigas)
Empty shells of the sword razor (Ensis ensis)
Anadara, a bivalve with taxodont dentition from the Pliocene of Cyprus