PARIS — Hanging in the sumptuous Grande Nef, or Great Nave, of the Musée des Arts Décoratifs in Paris are nearly 1,500 spindly strips of black plastic slotted together to form a gigantic screen. Each one resembles a short strand of seaweed, which is why its designers, the brothers Ronan and Erwan Bouroullec, named it Algue, the French word for seaweed.