Shipworms

The shipworms are marine bivalve molluscs in the family Teredinidae: a group of saltwater clams with long, soft, naked bodies. They are notorious for boring into (and commonly eventually destroying) wood that is immersed in sea water, including such structures as wooden piers, docks and ships; they drill passages by means of a pair of very small shells borne at one end, with which they rasp their way through. Sometimes called 'termites of the sea', they also are known as 'Teredo worms' or simply Teredo, from the Greek τερηδών teredōn, via Latin. Eventually biologists adopted the common name Teredo as the name for the best-known genus. Removed from its burrow, the fully grown teredo ranges from several centimetres to about a metre in length, depending on the species. The body is cylindrical, slender, naked and superficially vermiform, meaning 'worm-shaped'. In spite of their slender, worm-like forms shipworms nonetheless possess the characteristic morphology of bivalves. The ctinidia lie mainly within the branchial siphon, through which the animal pumps the water that passes over the gills. The two siphons are very long and protrude from the posterior end of the animal. Where they leave the end of the main part of the body the siphons pass between a pair of calcareous plates called pallets. If the animal is alarmed, it withdraws the siphons and the pallets protectively block the opening of the tunnel. The pallets are not to be confused with the two valves of the main shell, which are at the anterior end of the animal. Because they are the organs that the animal applies to boring its tunnel, they generally are located at the tunnel's end. They are borne on the slightly thickened, muscular anterior end of the cylindrical body and they are roughly triangular in shape and markedly concave on their interior surfaces. The outer surfaces are convex and in most species are deeply sculpted into sharp grinding surfaces with which the animals bore their way through the wood or similar medium in which they live and feed. The valves of shipworms are separated and the aperture of the mantle lies between them. The small 'foot' (corresponding to the foot of a clam) can protrude through the aperture. The shipworm lives in waters with oceanic salinity. Accordingly, it is rare in the brackish Baltic Sea, where wooden shipwrecks are preserved for much longer than in the oceans. The range of various species has changed over time based on human activity. Many waters in developed countries that had been plagued by shipworms were cleared of them by pollution as the industrial revolution and into the modern era; as environmental regulation led to cleaner waters, shipworms returned and became a problem. Climate change has also changed the range of species; some once found only in warmer and more salty waters like the Caribbean have established habitats in the Mediterranean. When shipworms bore into submerged wood, bacteria (Teredinibacter turnerae strain ATCC 39867 / T7901) in a special organ called the gland of Deshayes digest the cellulose exposed in the fine particles created by the excavation. The excavated burrow is usually lined with a calcareous tube. The valves of the shell of shipworms are small separate parts located at the anterior end of the worm, used for excavating the burrow. Shipworms are marine animals in the phylum Mollusca, order Bivalvia, family Teredinidae. They were included in the now obsolete order Eulamellibranchiata, in which many documents still place them.