Do a search, this topic has been disucssed hundreds of times so you'll find some great information. However, they are perfectly harmless and great additions to any tank to help act as part of the clean-up-crew. There are, though, many different types of these warms some which are harmful and some which are wanted in our tanks, the harmful ones are very rare to find. Most people will get rid of Bristleworms that are relatively big (3-4+ inches), I leave them though.
Rock Anemone
