An empty Channel Apple Snail Shell on the dried flats.
But not to worry about our Apple Snail population which is the favorite food of Limpkins.
When the flats dry out, they just bury themselves in mud, close their shells up tight (they have a trap door which is called an operculum) and they go to sleep until conditions are better again. In this sleeping state they can actually last for years.
Apple Snails are good survivors!