In a large pot, bring 4-5 quarts of salted water to a rolling boil. Add the small pasta variety and cook according to package instructions until al dente, about 8-10 minutes. Drain and rinse under cold water.

While pasta cooks, heat a skillet over medium-high heat. Add fresh shrimp and sauté for 2-3 minutes until pink and opaque. If using pre-cooked shrimp, chop into bite-sized pieces.

Dice celery, red bell pepper, and red onion into small pieces. Mix in a large bowl and chop parsley for garnish.

In a separate bowl, combine mayonnaise, sour cream, Dijon mustard, lemon juice, Old Bay seasoning, salt, and pepper. Whisk until smooth and creamy.

In the bowl with diced vegetables, add cooled pasta, shrimp, and imitation crab. Drizzle the dressing over and gently toss everything together.

Cover and refrigerate for at least 1 hour to let flavors meld. Chill longer for better flavor integration.

Before serving, stir gently, garnish with parsley, and serve on lettuce or in individual bowls.