Cut the squid or cuttlefish tubes in half lengthwise, then cut each half into thin strips (not rings).
Place the strips into a small bowl. Sprinkle with a few drops of lemon juice and refrigerate for at least 30 minutes.
Prep the bivalves
Unless your clams and mussels are farm raised, soak them in cold, well salted water for an hour and then rinse them, before proceeding. (Don't do this with your oysters.)
Shuck the oysters, clams and mussels, trying to avoid losing as much of their juices as possible. Leave them 'on the half shell'. Place on a tray and refrigerate until needed. (See Notes for details.)
Prep the shrimp
Shell the shrimp, leaving the tail on if you like. Immerse the peeled shrimp in a bowl of ice water with a few drops of fresh lemon juice and place in the fridge for about 30 minutes.
Assemble and serve the dish
Cover the bottom of a platter large enough to hold all the seafood in a single layer with a bed of crushed ice. This keeps the seafood nicely chilled but also keeps to hold the bivalves upright.
Place the clams, mussels and oysters all around the edges of the dish.
Then place a lettuce leaf or two in the middle of the platter. Lay top the squid/cuttlefish 'tagliatelle' on top.
Finally, arrange the shrimp in a decorative pattern around the tagliatelle, with one unshelled shrimp on top for decoration.