Edible bivalve mollusc (6)
I believe the answer is:
cockle
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">edible bivalve mollusc</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 cockle that I've seen before include "Burrowing mollusc" , "Edible bivalve mollusc" , "occupant of shell" , "Seafood item" , "Common edible bivalve" .)