Saute onion till translucent add garlic simmer 3 minutes.
Toss in pepper flakes.
Add tomatoes and parsley.
Stir in scallops and clams cover and simmer over low heat.
Meanwhile, in a large pot of boiling salted water, cook the capellini until just al dente, about 3 minutes. Drain; transfer to the scallops and clam mixture toss well adding pasta water if needed and serve immediately. Top with additional olive oil and garnish with fresh parsley.