What is it?

[Noj]

Hey everyone, I dont have a pic of this thing....YET.

But I will do my best to describe it. It moves only in the dark (crossed my tank in the pitch black, I am assuming at least, because today I can see one arm/leg/tentacle/something peaking out of a crack on the other side of the tank). It is a dark green in color, it has a bunch or arms/legs, at least 4 or 5, haven't seen them all, but have seen them poking out of 4 different cracks in the rock. It almost looks as though it would be a star fish, but it moves way too quickly. Legs kind of look like a fern.

Hope someone can explain this? My tank is cycling right now and this thingy obviously came in with my live rock.

A few other things I'd like you all to identify, but I wont ask those questions until I capture a picture of this little creeper.