The teredinids, commonly known as teredos or shipworms, are bivalve molluscs adapted to boring into wood. They are most closely related to the Family Pholadidae, or piddocks, which bore into mud, stone and coral. The teredinids have a relatively small, hemi-spherically shaped shell, the elongated body extending beyond the posterior end of the shell valves. The soft body, protected by the wood and the calcareous sheath the mantle secretes, contains most of the visceral mass posterior to the posterior adductor muscles. The siphons, which protrude from the burrow into the water for respiration and feeding, are relatively short. At their base are calcareous structures called pallets which seal off the burrow when the siphons are retracted. The shell valves, which function as a grinding tool during the boring action, gape anteriorly for the protusion of the foot and posteriorly for the protusion of the elongated body. As the anterior and posterior adductor muscles contract alternatively, the valves rock around the dorsoventral axis on their dorsal and ventral condyles. The foot holds the denticulated valves close to the head of the burrow so that. small particles of wood are rasped off when the posterior adductor muscles contract.

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