Just observing one of my new acro frags tonight (a smooth skin) and saw what looked just like a feather duster worm popping in and out of a bump on the frag. Every few seconds it would pop out with its fan and then quick as a flash go back inside. Although it was the only one of its kind on the frag, it blended in perfectly with the rest of the coral. Same color, just kind of an unusual bump. I'm not aware of any polyp that behaves like this but who knows? Is it just a very well camouflaged duster encrusted on the frag? I would post a picture but I couldn't get a good one. I figure just a description of the behavior would be enough. Do acros ever have little feather duster like polyps that poke in and out of the coral?