Answer:
The shared derived characteristic that can be written at point X is "cell walls made of chitin." This characteristic is shared by the Fungi kingdom, as well as some other groups like insects and crustaceans. Chitin is a tough, protective material that provides structural support to the cells of these organisms. While some other groups like plants also have cell walls, their cell walls are made of different materials like cellulose, so "cell walls made of chitin" is a characteristic that is unique to the Fungi kingdom and their relatives.