Worms!

[jordsy]

I just got my new tank set up. I was watching the tank one night and I saw a shirmp of some kind. So im using a bottle trap with some shrimp in it to try and catch it. While obseriving it i notice TONS of worms trying to get at my bait. They are as long as 30 sm streched out. They are brown and kinda flat with many spines along the sides. They live in the live rock and only come out at night. what are they and are they harmful to my tank?