3. Locate the small, round yellow or red hard plate on one side of the central disc. This is the madreporite, a perforated plate that functions as an intake valve for the water-vascular system within the body. The madreporite is also called the sieve plate. Therefore, the madreporite’s job is to bring water into the body for respiratory purposes.
4. Two rays are nearer to the madreporite than the rest; these are called the bivium. The other three rays are called the trivium. In the very center of the aboral surface is the anus, which may be hard to see. You may be able to use a probe to locate it. If you locate it, the probe will easily go down inside the starfish through the opening.
5. At the end of each arm or ray is an eyespot containing red pigment which allows the starfish to sense and respond to light. In preserved specimens, the eyespot can be located with a magnifying glass or dissecting scope by spreading the tube feet at the tip of the ray.