ID - No pictures O_o

[Nemain]

Last night as I was watching my tank, I saw a LONG ( about 2 cm :P) arm poke out of a whole in my blue sponge. It was sort of a creamy brown color with black rings on it. My interest was peeked and I watched it for another hour before exhaustion wore on me, but i saw 2 more arms poke out.

I believe it may be a star of sorts. Is there a way to get it to come out of the sponge? And if I do, what do I do with this creature?