Lugworms (Family Arenicolidae) were among the first polychaetes ever to be described. Some species of lugworms are such active diggers that an average-sized worm can irrigate its burrow by pumping water through at a rate of about 90 ml (3 oz ) in 10 minutes. Most species of lugworms are mass spawners, though a few are known to brood juveniles in their burrows or produce mucus cocoons attached externally to the burrow by a stalk.

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