Seafood that comes from reefs, di scoglio, is often more prized than their relatives that live around the bottoms, as in the small triglie di scoglio (red mullet), famous in Puglia. It's the same for octopus.
But now, al scoglio is often used for any dish that involves shellfish: spaghetti allo scoglio features molluscs and crustaceans (prawns, mussels, clams, garlic, octopus, tomatoes and parsley).
Image by Antonio Castagna