This is a refined version of the classic seafood stew. Serve as a first course, giving each person a variety of seafood.
Heat oil in a large pot over medium-high heat. Add onion, garlic, and bay leaf. Cook until onion is translucent, about 5 minutes. Add oregano, parsley, and red-pepper flakes. Cook 1 minute. Add wine, stock, clam juice, and tomatoes. Reduce heat; simmer gently 30 minutes. (You can make soup to this point up to 2 days ahead, and chill. Reheat; add seafood.)
Add clams; cook, covered, for 10 minutes. Add mussels; cook, covered, checking often and using tongs to transfer open clams and mussels to a bowl. Discard any that do not open. Add scallops, cod, squid, and shrimp to pan; simmer gently until seafood is cooked through, about 5 minutes. Gently stir in cooked clams and mussels; ladle into bowls, and serve.