Here on the Black Sea in Romania people are eating a shellfish called in Romanian "rapane" which they translate as "oyster" when I ask.
But they are elongated spiral shells which to me look nothing like the chunky flattish oyster shells in Australia. Besides which there is another Romanian word "stridie" for oyster and I can't find "rapane" in my print dictionary or any online dictionary. One person told me these are "sea oysters" as opposed to "ocean oysters". I've also been told they're not a native local species.
Here is a photo of a dead rapane shell on the beach and another of raw rapane waiting to be cooked: