How often has a casual stroll along a Tasmanian Beach resulted in a pocketful of shells that you wish you knew more about? How many species of cowrie have you got sitting in that jar of holiday treasure?

How different are winkles and whelks, scallops and oysters, cockles and mussels?  Are all those limpets on the rocks the the same species? Is that screw-shell native? Are all abalones the same? What shell species went into making that necklace?