Cook the pasta by bringing a large pot of salted water to a boil, add pasta and cook until al dente. Drain and rinse under cold water.

Prepare the shrimp by boiling water, then adding shrimp and cooking until pink and opaque; drain and cool.

Chop the imitation crab, celery, red bell pepper, and red onion, combining them in a bowl.

Make the dressing by whisking together mayonnaise, sour cream, Dijon mustard, lemon juice, and Old Bay seasoning in a bowl.

Combine cooled pasta, shrimp, imitation crab, and chopped veggies in a large bowl. Add the dressing and toss gently.

Chill in the refrigerator for at least 1 hour before serving, garnishing with parsley.