Final answer:
The madreporite in brittle stars is a small porous plate located on the upper surface of the central disk. It serves as the entrance for water into the stone canal, which is part of the water vascular system.
Step-by-step explanation:
The madreporite in brittle stars is not typically large, as it is a small porous plate located on the upper surface of the central disk. The madreporite serves as the entrance for water into the stone canal, which is part of the water vascular system in brittle stars. This system helps with circulation and movement in echinoderms, including brittle stars.