I bit hard to see, but I believe these are common bristle worms - good members of the cuc, can get back in the rock & eat debris where snails can reach.
here an example - where you can see better details
I agree with it looking like a common bristleworm. I think most SW tanks have them (that's what makes them considered common )
I usually leave them in my tank unless I see a really large one that I can easily remove. If you do remove them: USE GLOVES & tweezers so you don't expose the "bristles" to your skin or fingers. They are like prickly cactus & leave spines in your skin. Ouch!!