For the last few weeks my ivory snail, Saffron didn't move at all. I figured she was dead and my mum said to just leave her. She started floating for 3 days and then sank to the back of my tank. I looked for her after 2 days of not really bothering and she's completely gone. The shell and everything. She couldn't have gotten out of the tank because it has a top on it and she was probably dead. My zebra snails all left their shells behind when they died and now Saffron's completely disappeared. Any suggestions?