Preheat your oven to 350°F (175°C).
Cook the pasta shells according to package instructions until al dente, then drain and set aside.
In a mixing bowl, combine the ricotta cheese, chopped shrimp, crab meat, Parmesan cheese, garlic, lemon juice, and oregano. Season with salt and pepper.
Stuff each cooked shell with the seafood mixture and place them in a baking dish.
Pour marinara sauce over the stuffed shells, covering them evenly.
Drizzle heavy cream over the top and sprinkle with extra Parmesan cheese.
Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes, or until bubbly and golden on top.
Let the dish sit for 5 minutes before serving to allow it to set slightly.
Garnish with fresh herbs, if desired, and serve hot.