Ok, first, deep breath.  You need to see what kind of bristleworm it is.  Bristleworms are actually a good part of a tank, they are great detrivores.  Fireworms on the other hand are not something you want and should be removed.  Fireworms are generally a more vibrant color and have much longer bristles.  Bristleworms can be bi colored, with a darker end and a more red colored end.  More than likely you have bristleworms, which are more common.