Shell is white, triangular in shape, inflated, and coarsely sculptured with ridges used for burrowing; reduced in size and permanently gaping. It covers only the anterior end of a much larger worm-like soft body. Generally 4 in (10 cm) in total length, but may grow as long as 2 ft (60 cm). Mantle secretes a calcareous lining for wood burrow. The posterior end has short siphons and unsegmented shovel-shaped calcareous pallets used to close the burrow. Stomach has a wood-storing caecum or blind pouch.
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