Bring large pot salted water to boiling for pasta. Combine marinara sauce, capers, mashed anchovy fillets and red pepper flakes in medium-size saucepan; cook over medium heat 10 minutes. Stir in chopped fresh parsley. Keep sauce warm.
Meanwhile, cook spaghetti following package directions.
Heat olive oil in large skillet. Season shrimp with salt and pepper. Add shrimp to skillet; saute over medium-high heat 2 minutes on each side, until cooked through. Toss pasta with sauce. Arrange shrimp on top.