Possible Clues:

• Piece of bread and a tin containing European crayfish, perhaps
• Lobster perhaps reddish? Serve in container
• Tin containing curate's chopped-up seafood
• A scarce nut is unusual life form with hard case
• Perhaps crab tin contains sign of decay: something one can't return
• Shelley may have sounded crabbed, but not like this
• eg Crab
• Shrimp, for one
• Eg, lobster
• Expert article on some bread and crab, for example