Saute onion and celery in skillet or dutch oven coated with cooking spray for about 5 minutes (or until tender).
Add minced garlic and saute another minute.
Add diced potato, 1/2 teaspoons salt, and 3/4 teaspoons pepper; cook another 2 minutes. Sprinkle flour over potato mixture and cook another minute or two.
Add clam juice and skim milk; bring just to a boil, stirring constantly, and then reduce heat immediately. Simmer for about 20 minutes, or until potatoes are tender.
With a slotted spoon, remove at least 2 cups of potato/celery/onion mixture. Puree and add back to soup.
Stir in remaining salt and pepper, as well as aniseseed and thyme. (Note re: anise -- it makes a big difference in flavor if you can buy whole aniseseed and grind it yourself. If not, just use bottled ground anise.) Simmer 10 minutes.
Add scallops and shrimp; cook about 5 minutes, or until shellfish are cooked.
Add half-and-half and cook a few more minutes, until heated thoroughly.