Some sort of Worm? HELP?

Sorry, can't really tell much from the picture. There are a number of worms that are in healthy marine tanks. Most are detrivores, cleaning up the tank and a re good thing to have. Very few parasites exist away from their host, so it's unlikely to be a parasite. I'd suspect that this is a small bristle worm--not a bad thing at all. They are covered in spiny bristles, so you should take care in handling them since some people react to the bristles and they can cause a rash. But, removing them is a) a losing proposition--they reproduce in our tanks and are very good at hiding b) they serve as a food source for some fish/crustaceans and c) most anything that cleans is welcome in my tanks. They can get out of control--this indicates too much food in the tank, so it's controllable. You'll also see some humdingers--I have one in my reef that is about 8-10 inches long, thicker than my pinky. Never bugs anything, just noses around and eats leftovers.

More likely good than bad.

Look at your tank a couple of hrs. after lights out. Use a red lens flashlight. If you think that worm is scary just wait till you see what else lives in there. I love looking at my tank at night. 1 of the benefits of lr.

Red Light is often used the most because not many animals can detect the red spectrum, so it looks like it is pitch black when you shine a red light (you an also use red tissure paper over an exhisting flashlight as well). The illuminescent lights tend to work as well, but are much more expensive.