The nervous system of a starfish has a "radial nerve" running through each arm and a "circumoral nerve" that goes around the mouth and connects to the radial nerves. The radial nerves control most of the starfish's actions. Each of the radial nerves has to cooperate with the other one in order for the starfish to do anything. There is a theory that one arm will completely take charge of the starfish and move it in the direction that it is sensing. They can use it to locate food and mates. They have learned to associate different textures, smells, and lighting with the presence of food.
Starfish reproduce by free-spawning, or just releasing their gametes into the water and hoping that a starfish of the opposite gender will fertilize it. To increase the chance of fertilization they usually group up when they're ready to reproduce. When the egg is fertilized they turn into bipinnaria larvae and then develop into brachiolaria larvae. While they are larvae they are plankton and unlike adults they are bilaterally symmetric. Then they undergo a complete change and become benthic and settle to the bottom.
From the outside you can't tell which gender a starfish is because the organs are located inside the arms.
From the outside you can't tell which gender a starfish is because the organs are located inside the arms.