>>22602690I have an idea for the first two stages. They could be based on sea slugs rather than snails right from the start, with an an anemone sort of thing on their back, and wouldn't gain a shell until the final stage (keeping with the idea of not gaining the rock type until the final stage)
As for the final evo, the dragon slug idea has potential. Maybe with a seal kind of look, or even some nautilus inspiration
I also found this
http://en.wikipedia.org/wiki/Hafgufa