My snail has had a growth on it for several months now that is getting progressivly larger. It seems to be building some sort of hard shell similar to a feather duster. Now it is curled up on mt snail and has an opening about the size of a pencil( a little smaller). It is an all white shell and the animal inside is also all white and I can see it move from time to time. It never pokes out of the tube. However it will let a very thin tentacle or string out that can stretch up to 6-8 inches. Does anyone know what this is, and should I get rid of it? Thanks.