The American piddock is an elongated white shell. It was introduced into the southeastern section of the North Sea at the end of the 19th century. It drills itself into wood and blocks of peat with the toothed ribs of its shell as grater. It doesn't eat the wood or peat, but filters plankton out of the seawater. Other piddocks also have the same lifestyle, even though they are not related to one another. The American piddock is displacing the indigenous white piddock and oval piddock.