Make vinaigrette: In a medium bowl, combine zest, juice, salt, and pepper. Gradually whisk in olive oil. Set aside.
Make mayo: In a small bowl, stir together all ingredients. Chill until used.
Cut cheeks from mangoes, peel fruit, and thinly slice crosswise. Cut remaining fruit from pits, peel, and thinly slice.
In a medium bowl, stir crab and shrimp with 2 tbsp. vinaigrette to blend.
In another bowl, gently mix mangoes and arugula with remaining vinaigrette. Spoon salad onto plates and top with crab mixture. Sprinkle with lime leaves. Serve mayo on the side to dot over salads.
*Buy shelled crab from a good fish market, or shell your own meat from a 1 3/4-lb. cooked crab (less pricey). Look for sustainable, wild Oregon pink shrimp. Find kaffir lime leaves at Asian markets.
Nutritional analysis is per serving with 1 tbsp. mayo.