Thaw shrimp, scallops and crabmeat, if frozen. Peel and devein shrimp, leaving tails intact, if desired. Rinse shrimp; pat dry with paper towels. Cut any large scallops in half. Set shrimp, scallops and crabmeat aside.
Scrub live mussels under cold running water. Using your fingers, pull out the beards that are visible between the shells. In a very large bowl, combine 2 quarts (8 cups) cold water and 2 tablespoons of the salt. Add the mussels; soak for 15 minutes. Drain and rinse, discarding water. Repeat twice. Set aside.
Strain shucked clam juice to remove bits of shell. Set clams and clam juice aside.
Cook pasta according to package directions. Drain; keep warm.
In a 4-quart Dutch oven, combine undrained tomatoes, mushrooms, parsley, wine, garlic, crushed red pepper and lemon juice. Bring to boiling; reduce heat. Simmer, uncovered, for 5 minutes.
Add shrimp, scallops, mussels, and shucked clams and juice (if using) to tomato mixture. Return to simmer. Cook, covered, about 5 minutes or until shrimp turn pink, scallops are opaque, mussel shells are open and mussels are cooked through (discard any mussels that do not open). Stir in crabmeat, canned clams (if using), basil, and oregano; heat through. Remove from heat. Season to taste with additional salt and black pepper.
Serve sauce over warm pasta. Sprinkle with Parmesan cheese. Serve immediately. Makes 6 servings.
Use 1-1/2 pounds any combination of shrimp, scallops, crabmeat and clams; omit the mussels.