Bivalve mollusc with fan-shaped shell (7)
I believe the answer is:
scallop
'bivalve mollusc with fan-shaped shell' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for scallop that I've seen before include "Edible bivalve mollusc" , "one may be in one's shell" , "Shell - sign of a pilgrim" , "Shellfish that's also plc" , "Shellfish - pilgrim badge" .)