Preheat the oven to 350°F. In a large pot of salted boiling water, cook lasagna noodles according to package instructions. Lay noodles flat on a greased baking sheet, separating layers with parchment paper.
In a large skillet over medium-high heat, heat the olive oil. Season shrimp with salt and pepper. Cook in the skillet until pink and opaque, about 2 minutes per side. Remove shrimp and chop into bite-size pieces.
Return skillet to medium heat and melt butter. Add garlic and thyme, cooking until fragrant, about 30 seconds. Stir in flour and cook for 1 minute. Slowly whisk in the half-and-half and clam juice. Simmer, stirring occasionally, until the sauce thickens, about 4 minutes. Stir in 1/2 cup Parmesan and season with salt and pepper.
In a medium bowl, mix ricotta, egg, remaining 1/4 cup Parmesan, and parsley. Season with salt and pepper.
To assemble the lasagna, spread a thin layer of sauce on the bottom of a large baking dish. Add a layer of noodles, spread the ricotta mixture over the noodles, and layer with shrimp, crab meat, and sauce. Sprinkle with mozzarella. Repeat the layering process for three total layers, finishing with a top layer of mozzarella.
Cover with foil and bake for 30 minutes. Remove the foil and bake until golden and bubbly, about 15 more minutes.
Garnish with fresh parsley. Let the lasagna cool for 15 minutes before slicing and serving.