If mollusk shells were accepted as a method of payment in modern-day markets, what economic role would they play in the financial system?

medium of exchange

Explanation:

Mollusk shells would probably be used as a medium of exchange, but cannot be considered money. In order for mollusk shells to be considered money, they have to serve the four functions of money:

serve as a unit of account serve as a store of value serve as a medium of exchange serve as a standard of deferred payment.