Orchid looking black feather duster?

What I have is some type of feather duster perhaps. First, it's shell seems to be a white calcium buildup with a tiny hole at the bottom front, it's on a piece of rock I recently acquired. Almost appears to be a tiny cave. What made me even notice it is, when I approach it quickly (from outside the tank) it pulls in. No feather duster I've seen does this. It gets spoked easily when I get close to the glass...Also, there seems to be two feather duster heads in opposite direction and what appears to resemble the flowers of that on an orchid flower. All dark brown and black in color. I have tried to take a picture but it won't let me lol. If I sit still long enough it will come out, or approach the glass near where it's located slow enough, it won't pull back in. Any clue. It's odd to be like a feather duster but then to have leafs like the flower of an orchid on the bottom... Does this make any sense?

 

Could be a barnacle? Not sure with out pics its hard to ID.

 

google Christmas Tree worm & see if that's it.