Appeal to get sponge cover for dish (7)

I believe the answer is:

scallop

I'm a little stuck... Click here to teach me more about this clue!

'for dish' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for scallop that I've seen before include "Shellfish that's also plc" , "Bivalve mollusc with fan-shaped shell" , "Mollusc or lacy edge" , "Marine bivalve" , "Shellfish - badge worn by pilgrims to Santiago de Compostela" .)

I've seen this clue in The Hindu.

Want a hint initially instead of a full solution? Install my app