Teredo navalis is a bivalve mollusc but appears worm-like due to its elongated body and reduced trilobed shell, which is specialised for wood boring. The shell is white in colour with its outer most layer (periostracum) light brown. The shell can be up to 2cm long and covers only the anterior end of the long, soft body. The valves of the shell are divided into different regions with various sculptures. The beaks are situated near the anterior end of the shell. The soft worm-like body is light brown in colour and up to 15 cm in length. It lies in a calcareous tube up to 60 cm long and 0.8 cm in diameter. The thin tube has a septa (dividing wall) near the opening. There are two small siphons at the posterior end of the body that are withdrawn and closed off by a calcareous pair of paddle shaped accessory plates (pallets), each off white in colour and up to 0.5 cm long.The trilobed, heavily ridged shells halves of Teredo navalis are used to drill through wood forming characteristic, winding burrows that are lined with chalky deposits. These burrows can be seen when the wood is split apart. The small holes can be up to 1 cm in diameter.
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