eeewwwwww!!!!! Snails. Slimy gooey ..... we have a lot of them here as well. They live mostly in my hostas and by the end of the summer they've munched on them so much the edges turn brown. The kind we have here do the same with their snotty trail. And the shells are black and yellow striped.I don't think they are as big as the ones you've photographed though.
I think the species you are describing is also present here. But those seen on the photos are really bigger. If I am honest I don't mind any if they are having houses. But if they don't, then I agree with you - ewww. 😉