Soak clams in cold water to remove grit. Drain. If needed, rinse and de-beard mussels.
Heat olive oil in heavy bottomed soup pot over medium heat. Add onions and leeks and cook until softened, about 5 minutes.
Add carrots and green or red pepper. Cook several more minutes.
Add garlic and tomatoes. Cook 1-2 more minutes, stirring.
Add wine, clam juice, and all herbs and spices (except salt and pepper). Bring to boil.
Add salt and pepper and potatoes. Reduce heat and simmer, covered, until potatoes are firm and tender, about 10 minutes.
Add chicken broth. Simmer for 5 minutes, covered.
Add clams. Cook at brisk simmer until clams open, 2-3 minutes.
Add fish and mussels. Simmer until mussels open, 2-3 minutes.
Add shrimp and scallops. Cook 1 minute more.
Add cream and parsley. Just bring to a boil. Serve with crouton slices.