In a dutch oven, over medium heat, brown pancetta till some of the fat has rendered. Add a tbs or 2 of olive oil if it seems too dry. Add onion, garlic, oregano and fennel seeds and sauce till onion is tender, about 8 minutes.
Add tomatoes, clam juice, wine wine if using and liquid drained from canned clams. Increase heat and boil until slightly thickened, about 15 minutes
Add clams, shrimp and crabmeat. Reduce and simmer for 5 minutes
Stir in basil if using. Season with salt and pepper to taste and serve.