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.