its the feather duster, they are worms in a tube, he came out of his. They do that sometimes when they're really stressed. Im not worried about it though, he has been like that for just over two weeks and he is still alive. Eventually he will grow his tube back or maybe find a hole in a rock somewere, but as of now he just bobs around my tank, kind of gross actually, it moves blindly, just like an earthworm.