Shipworm

Shipworms, or teredo worms, are marine bivalve mollusks in the family Teredinidae that eat wood submerged in saltwater. Despite their long, worm-like shape, which makes their clam-like classification hard to spot, sailors have long called them "worms"—a name echoed in English and German (Schiffsbohrwurm). They are infamous for burrowing into and wrecking any wooden structure in seawater, such as piers, docks, and ships, which is why people sometimes call them "termites of the sea." Carl Linnaeus gave the name *Teredo* (from the Greek for "wood-worm") to the best-known genus in his 1758 *Systema Naturæ*. One species, *Kuphus polythalamia*, can grow over 1.6 meters long and 7 centimeters wide, making it one of the largest bivalves on Earth. It eats wood until maturity, then settles into marine sediment and relies on symbiotic, sulfur-eating bacteria for food. Another species, *Lithoredo abatanica*, burrows into and feeds on limestone in freshwater.

Depending on the species, an adult shipworm ranges from a few centimeters to about a meter long. The average is 10 to 15 centimeters in length and less than 6 millimeters wide, though some, like *Kuphus polythalamia*, reach over 1.6 meters and 7 centimeters in diameter. The body is cylindrical, slender, and worm-like, but shipworms still have recognizable bivalve parts: valves, gills (ctinidia), a mantle, and siphons. The gills sit mainly inside the branchial siphon, which pumps water over them. Two long siphons stick out from the rear end, passing between a pair of calcareous plates called pallets. When alarmed, the animal pulls its siphons in, and the pallets block the tunnel opening. The two valves are at the front end, used for boring into wood. They are roughly triangular, concave inside, and convex outside, often with sharp grinding surfaces. The valves are separated, with the mantle opening between them, and a small foot can poke through. Bacterial symbionts in a gut organ called the typhlosole help digest wood. One group of bacteria, *Alteromonas*, digests lignin, breaking down the tough layers around cellulose so other enzymes can access it. Another species, *Teredinibacter turnerae*, in the gills, releases cellulose-digesting enzymes that may enter the gut through the gland of Deshayes. These work with the shipworm's own enzymes to digest wood. The burrow is usually lined with a calcareous tube. The shells are small and at the front, used only for digging; they no longer protect the animal, which spends its whole life inside wood.

*Teredo navalis* develops from eggs to larvae in about five weeks, half of that time in the mother's gill chamber before being released as free-swimming larvae. Their sexes alternate: young are hermaphrodites, while adults can be male or female. Typically, they start as males and later become females. A second male-to-female phase is possible, but shipworms rarely live long enough for it. Their lifespan is one to three years. Shipworm anatomy includes typical bivalve organs, though shaped by the long, thin body. The gills are split into a small front half and a larger rear half, linked by the digestive tract. The heart-kidney system is tilted, putting the kidneys above the heart, with the atria behind the ventricle. The anterior and posterior aortas swap positions. The anus opens at the end of a long tube. The digestive gland has several parts with separate openings into the stomach, and a large caecum connects to it. The digestive tube includes the gland of Deshayes, likely a salivary gland, which links to the esophagus and stretches along the back of the body.