Simplify the following text for a Grade 7 native English-speaking person.
Original: Cypraea moneta ) were used as a currency in Africa ( Ghanaian cedi in Ghana named after cowry shells ) and elsewhere , such as in China where the shell or copies of the shell were in theory used as a means of exchange .
Simplified: The Ghanaian unit of currency known as the Ghanaian cedi was named after cowry shells . Starting over three thousand years ago , cowry shells , or copies of the shells , were used as Chinese currency .