A. The first thing you need to do is identify what it is you have. They may be Bristleworms, because these are often found hitchhiking in on live rock, so it is not all that uncommon. If they are Bristleworms, depending on what type you have they may need to be removed from the tank. Some are beneficial Bristleworms, but for those that are not, if left alone they can overrun your tank and cause irritation and other problems for your tank inhabitants. They multiply rapidly and some are carnivorous, hence they may need to come out.
Make sure that you do not touch them, as their bristles are very thin and will embed themselves in the skin and result in severe itching. Traps with food in it are usually the way to remove them. For more detailed information about what Bristleworms look like, different types, and how to remove or control them with various trap methods or by means of natural predators, refer to Bad Type Bristleworms Control.