Cushion starfish. Close-up showing the top surface of a cushion starfish (Culcita novaeguineae) from above. Most starfish have five arms and the mouth is located on the underside. The upper surface is called the aboral or dorsal surface. The small, pale orange structure at upper right is called the madreporite. It acts as a water filter and supplies the starfish's vascular system with water so that it is able to move. The white patches are known as pedicellariae, which prevent other organisms from colonising on the stafish.