Mussels or crabs, eg (9)

I believe the answer is:

shellfish

(Other definitions for shellfish that I've seen before include "Oysters, cockles, mussels etc" , "Category of seafood" , "Lobsters, cockles, mussels etc" , "Crustaceans" , "A shrimp, maybe" .)

I've seen this clue in The Times.

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