Shell sometimes used as money (6)
I believe the answer is:
cowrie
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">shell sometimes used as money</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cowrie that I've seen before include "Mollusc (shell used as money)" , "Shell once used as currency" , "Marine gastropod with a shiny shell once used as money in some parts" , "Brightly marked seashell" , "Shell sometimes used as form of money" .)