You have probably found the spiraled shells of gastropods, or sea snails while walking along Outer Banks beaches.  Whelks, moon shells or shark's eyes, and periwinkles are all gastropods, one-shelled or univalve mollusks.  What you might have also discovered with out knowing it is a gastropod operculum.

When a soft bodied sea snail retreats into its shell, it is the hard disk shaped operculum which is left exposed to the outside world and deterring predators.  They get their name from the Latin for lid or cover.  Keep your eyes open for them this summer.