Green brittle starfish

I was at the lfs today buying saltwater to do a water change when suddenly a coral caught my eye, It was a kenya branch coral. The guy broke off a little piece of it with life rock and put it in a bag. When I got home, I then proceded to aclimate the corals and dip them, and soon, I saw something odd, it was a brittle/serpent starfish! Free starfish! I said. Then I glued the coral and put the starfish in my tank, and immediately hid in a rock. Again. I should've done research because it might be a green brittle starfish which I heard may eat fish. It is very small, should I take it out, should I be worried? I currently can't see it but from what I have read, it should come out after I turn of the light. If I get it out, can I put him in my sump for now?