This certainly is not a common occurrence, but I have seen a couple of other
cowries with glazed-over barnacles, as well as one with a glazed-over
tubeworm.  The question that intrigues me is why the cowrie waited until
it's guest was a full-grown barnacle to glaze it over.  Why didn't the
cowrie glaze over the barnacle while it was still a near-microscopic,
freshly attached spat?  This is probably the reason why such encrustations
are so uncommon on cowries.  So why does an occasional larval encrusting
organism manage to escape this fate and grow to maturity, and presumably get
glazed over only after it dies?

Paul M.