Each ray of a sea star has a light sensitive organ called an eyespot. Though it can not see nearly as well as we do, sea stars can detect light and its general direction. They have some idea of where they are going. Given enough time, sea stars can grow back arms that have been damaged or removed. For most sea stars.
Sea stars eat many things.
Many sea stars eat mussels and clams in an interesting, yet disgusting way. This creates an opening between the two shells that is only .01 inches wide. Using this tiny gap, the sea star then puts its stomach into the clam's shell . Once this happens, the mussel or clam dies. When it is done, nothing is left but an empty shell.