Wash all seafood well and set aside.
Heat olive oil in a large frying pan over medium-high heat. Add garlic and saute lightly, about 30 seconds. Add clams, mussels, and 4 teaspoons parsley and cook for 3 to 4 minutes. Add calamari, shrimp, salt, and red pepper and cook for 2 minutes. Add wine, stir, and then let some of the liquid evaporate for 2 minutes. Add tomato sauce and remainder of parsley and stir well.
While sauce is cooking, cook spaghetti in a large pot of boiling salted water until al dente. Drain pasta and add to pan with sauce. Toss well and serve immediately.