In a large salad bowl toss together salad greens, fennel, and celery. Top with shrimp and lobster. Set aside.
In a food processor bowl or blender container combine parsley, mayonnaise or salad dressing, sour cream, yogurt, green onion, vinegar, basil, anchovy paste or anchovy, garlic, and tarragon. Cover and process or blend until nearly smooth.
Drizzle 1/4 cup of the dressing over salad. Toss gently. Top with edible flowers, if desired. Serve immediately. Pass remaining salad dressing. Makes 4 main-dish servings.