Marine bivalve (6)

I believe the answer is:
oyster
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">marine bivalve</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for oyster that I've seen before include "Bivalve that may nurture a pearl" , "Succulent bivalve, may bear a pearl" , "Pearl-producing bivalve" , "Food shellfish" , "Type of mollusc" .)