I've never seen one with the foot extended. In fact, I mostly find empty shells or sometimes just the operculum washed up in the wrack. The empty shells are popular with hermit crabs.
|Moon Snail Shell|
I did find one last week that was in its shell with the operculum tightly closed.
|Moon Snail -- Operculum Tightly Closed|
|Operculum Washed up against a Rock|
|Part of a Sand Collar|
The sand collars are made up of the snail eggs sandwiched between layers of mucus coated with sand . They look fairly solid, almost like rubber gaskets sometimes, but there's more to them than is immediately visible.
|Sand Collar Closeup|
|Sand Collar with Eggs Showing|
|More Partial Collars with Eggs|
|Clam Shell with Countersunk Hole Drilled by Moon Snail|
Oh, and the main predators of moon snails are gulls.