A superstructure was the upper portion of a constructed building or ship.
The superorganism that inhabited Murder Planet in the Hirogen star system was originally identified as a cilium-like vegetation. This vegetation had the ability to fabricate the desires of its intended victims onto its cilium. In 2383, it used its cilia to entangle the nacelles of the USS Protostar then used them to infiltrate the ship's ventral superstructure. (PRO: "Dream Catcher")