[2] It contains marine polychaete species that live in mud, holes bored in rocks, and holes bored in the shells of shellfish.

[3][4] Some shell-[5] and rock-boring[citation needed] polydora worms leave a characteristic double hole in the rock and shells in which they burrow.

[1][6] Polydora species are a major economic issue for parts of the shellfish industry.

Although this makes the oyster grow much more slowly, and makes the shell ugly and harder to sell, the meat of the oyster is still fit to eat.

[5] In Australia, the Native flat or mud oyster, Ostrea angasi, became locally extinct, in estuaries on the East Coast north of the Clyde River, as a result of the accidental introduction of the mud worm, Polydora websteri, with Saccostrea glomareata spat from New Zealand, from 1888 to 1898.