Bring a large pot of water to boil and cook pasta according to package directions. Reserve 2 cups of pasta water.
In a medium-sized saucepan over medium-high heat add the butter. Add the scallops and cook for 2-3 minutes and add the shrimp for the last 1-2 minutes and cook until no longer pink. Remove and set aside on a plate.
Add the reserved water to the saucepan and bring to a boil. Add the mussels and reduce to a simmer and cover. Let the mussels steam for 5 minutes. Discard the ones that didn't open. Set aside with the shrimp and scallops.
To make the creamy lemon sauce:
Add 1/4 cup butter to the saucepan and melt. Add garlic, heavy cream, chicken broth, and cream cheese. Stir until cream cheese has melted and is smooth and creamy. Add the parmesan cheese and juice of one lemon and let simmer until it has thickened.
Stir in pasta and seafood and stir until heated through. Serve with fresh chopped parsley and parmesan cheese if desired.