I have a little colony of tiny feather dusters; they have been doing great the past few weeks they were open 24/7. Earlier this week one of their tubes completely disappeared and I found it across the tank, the duster was still there though and was feeding and everything, but this morning it was completely gone (tube and worm). I don't know how it moved in the first place because they have to leave the tube to move. The rest of the worms remain either half closed or completely closed. WHAT IS GOING ON??