i just got a rock w/some button polyps and shrooms on it. it also has some arms coming out of small holes in the rock. they are white, with black bands and the arms look to be spiny. they almost appear to be like brittle star arms, but the holes that they're coming from are no bigger than the arm itself. i can't figure out the photo thing, so i can't post one. these things just sort of sway in the currents. any ideas?