Looks like a common Bristle Worm to me. They are good members of the CUC (clean up crew) but the kinda gross people out & scare some. If you remove him from your tank...don't use bare fingers. The bristles will get stuck in your skin (like a splinter )
If you over feed & have lots of food for them...you may start seeing lots of them. If not, you may only see a few.