In a 4-quart pot, steam the clams in the water until they are all open, about 10 minutes. Scoop out the clams and remove the top shell from each one. Gently cook the garlic in olive oil in a saucepan for 4 minutes and carefully pour in the clam-cooking liquid, leaving the sand behind in the pot. Add the parsley and season with freshly ground pepper to taste. Put the clams in the same sauce and cover to keep the warm. Boil and drain the pasta, divide among hot bowls, and ladle on the calms with their sauce.