1.Heat the olive oil in a large saucepan over medium heat. Add the onion and garlic, and stir for 5 to 8 minutes until the onions are translucent. Season the onions and garlic with salt and pepper.
2.Add the anchovies and the tomato paste and cook for about 2 minutes, breaking up the anchovies with a spoon. Stir in the tomato sauce, crushed tomatoes, ΒΌ cup parsley, 1/4 teaspoon red pepper flakes, 2 teaspoons salt, Italian seasoning, and white wine. Bring the contents of the saucepan to a boil, then reduce the heat and simmer for about 15 minutes until the sauce has thickened.
3.Meanwhile, bring the water to a boil in a separate stockpot over high heat. Add 1 tablespoon salt then the linguine to the boiling water and cook it until it is barely al dente, about 6 minutes. Drain the pasta, reserving about 1 cup of the pasta water.
4.Add the clams to the saucepan and cook them until they open, about 8 to 10 minutes. Transfer the clams to a large bowl, discarding any that did not open. Add the mussels to the saucepan and cook them for about 3 to 5 minutes, until they open. Transfer the cooked mussels to the bowl with the clams, again discarding any that did not open.
5.Bring the sauce back to a boil, then add the shrimp and scallops and cover the pan. Remove the pan from heat and let it sit for 5 to 8 minutes until the shrimp and scallops are just about cooked through.
6.Return the pasta sauce to the stovetop and bring it to a boil. Add the cooked pasta and 1/4 cup of reserved pasta water to the pan, and simmer for about 2 minutes until the sauce thickens. Add more water as needed.
7.Season the dish with salt, ground pepper, and red pepper flakes to taste. Transfer the pasta mixture to a large bowl. Arrange the cooked clams and mussels over the pasta and garnish with the remaining fresh parsley.