I would say that catch the light... There is no tube, when it retracts, you cannot even tell where it came from - I guess it retracts right into the rock.
I have that SAME thing in my tank here at home. It's on the back of a rock and only feeds now and again. It's got a number of Tree Branch like arms that extend out. Then one at a time it "rolls" one up and extends another. Just the other day a local reefer was asking me about a strange "critter" and he described the same thing. Mine has grown considerably since I first saw it and I have seen other much smaller ones scattered around my life rock.