I found all this in minutes on the beach:
What are they? Opercula! These are the ‘doors’ used by gastropods to close the shell aperture for added protection (mostly from predators, but also from dessication for intertidal snails and terrestrial prosobranchs).
I really wish I had a photo of the beach; there is a thick layer of debris near the high tide line, full of unrecognizable bits of shell and coral, but also filled with these distinct round, polished bits – like pearls. They are obviously resistant, but its hard to tell how much wear could occur on the edges without it being obvious.
I can’t be sure of the species, but I did collect several shells like this nearby, with a round, calcareous operculum:
So that’s pretty cool right? Yeah. I think so, but then I came across something special!
There was one in the pack that was distinct. At first I thought it was chipped, but looking at the shape of the spiral (the inside), and the bulbous exterior surface makes me wonder if this wasn’t some severely damaged individual – snails sometimes grow their shell a bit misshapen after serious shell damage. It could simply be another species, but most members of Turbo‘s family Turbinidae have round apertures, and the operculum is fairly distinct (as far as my limited experience knows). The other option is some mutant Turbo with a wonky aperture, or simply a disjointed operculum mechanism.
I really wish I had the shell… *sigh*
PS Wikipedia had this neat link about the history of operculum use in the middle east.