Bring water to a boil; add shrimp, and reduce heat. Simmer 3 to 5 minutes. Drain well. Peel and devein shrimp.
Grind shrimp or reduce almost to a paste in a food processor. Add butter; blend well. Stir in mayonnaise, Worcestershire sauce, lemon juice, mace, salt, pepper, and hot sauce.
Lightly oil a 4-cup fish mold, and line with plastic wrap. Pack shrimp mixture firmly into mold; chill several hours or overnight. Turn out onto a serving dish, and peel off plastic wrap. Sprinkle with paprika. Garnish with parsley, lemon slices, and pimiento, if desired. Serve with crackers.