1 1/4 lb Unpeeled large fresh shrimp 1/2 lb Sea scallops 1/2 c Chablis or other dry white - wine 2 cn Standard oysters, drained - (10-ounce) 1/2 c Dry white vermouth 1 tb Finely chopped onion 1/4 c Plus 2 tbs. butter or - margarine, melted 1/4 c All purpose flour 2 c Milk 2/3 c Grated parmesan cheese 1/2 c Shredded gruyere cheese 1/2 c Shredded swiss cheese (2 oz) 1/4 ts Salt 1/4 ts Pepper 1/8 ts Ground nutmeg 1/2 c Crushed round buttery - crackers 1/4 c Butter or margarine, melted Paprika Chopped fresh parsley Peel and devein shrimp. Combine shrimp, scallops, and wine in a medium skillet; bring to a boil. Reduce heat, and simmer 3 minutes; drain well. Set shrimp and scallops aside. Repeat procedure with oysters and vermouth. Combine shrimp, scallops, and oysters, and spoon evenly into 4 lightly greased individual baking dishes. Cook onion in 1/4 cup plus 2 tbs. butter in a heavy saucepan over medium-high heat, stirring constantly, until tender. Reduce heat to low; add flour; stirring until smooth. Cook 1 minute, stirring constantly. Gradually add milk; cook over medium heat, stirring constantly, until mixture is thickened and bubbly. Add cheeses, salt, pepper, and nutmeg, stirring until cheeses melt. Spoon sauce evenly over seafood mixture. Combine cracker crumbs and 1/4 cup melted butter; sprinkle evenly over casseroles. Sprinkle with paprika. Bake, uncovered, at 350 for 20 to 30 minutes or until golden and thoroughly heated. Garnish, if desired with chopped fresh parsley.