Teredo navalis, commonly called the naval shipworm or turu,[2] is a species of saltwater clam, a marine bivalve mollusc in the family Teredinidae.

Like other species in this family, this bivalve is called a shipworm because it resembles a worm in general appearance while at the anterior end it has a small shell with two valves, and it is adept at boring through wood.

It tunnels into underwater piers and pilings and is a major cause of damage and destruction to submarine timber structures and the hulls of wooden boats.

Teredo navalis has an elongated, reddish, wormlike body which is completely enclosed in a tunnel it has made in floating or submerged timber.

[4] Dispersal to new habitats occurs both during the free-living larval stage, by floating timbers carried along by currents, and, historically, from the hulls of wooden vessels.

[6] Food particles, mostly timber raspings but also some microalgae, are extracted from the water passing through the gills where gas exchange also takes place.

When it has formed a hollow, it undergoes a rapid metamorphosis, shedding and consuming the velum and becoming a juvenile shipworm with small horny valves at the anterior end.

[8] In their gills, shipworms house Teredinibacter turnerae, a symbiotic bacterium which converts nitrogen (dinitrogen) from the water into a form usable by its host, essential for survival on nitrogen-poor diet of wood.

It has spread in the Pacific Ocean where its greater tolerance of low salinity levels has caused damage in areas previously unaffected by native shipworms.

[6] In the eighteenth century, the Royal Navy resorted to coppering the bottoms of its ships in an attempt to prevent the damage caused by shipworm.

Experiments by the Dutch in the 19th century proved the inefficacy of linseed oil, metallic paint, powdered glass, carbonization (burning the outer layers of the wood), and any of the usual biocides such as chromated copper arsenate.