Hacksaw looking worm: Safe or Not?

[Mr Cob]

Hey maastards I just bought a little zoanthid attached to a small piece of rock and once I added it to my tank I watched a brownish looking worm several inches in length begin to crawl out of the rock.

He kind of looks like a hacksaw al the way around.

I removed the rock and of course he's hiding now, but I wanted to find out if this guy is safe or not before putting it back into my tank.

I have a 120gal with LR and Softies.

Thanks,
Rob