Hi All. I bought some live rock the other day and there was a large coiled tube with an open end about 1/2 inch across sitting on the side of the rock. The shop claimed this was a feather duster and looking inside you can see something black with white spots moving around and sometimes it comes right to the lip of the opening and if you shine a light at it it retreats back into the hole. Does this sound like a feather duster and should it be coming out? I have had it for over a week now. It is in a well lit spot, are there particular conditions these things like?