This protects them from predators and crashing waves. They can change direction without turning around. Tube feet are also used for prying open mussels and clams. Some sea stars will insert their stomachs into the shell and digest their prey. When finished, the sea star retracts its stomach and moves on.
Sea stars can regenerate new rays when broken.
Life span varies with species from 5 to 20 years. They attach themselves to rocks by secreting a viscous liquid that quickly hardens to form a fibrous thread called byssus. If removed from the rocks, a mussel will die. A mussel lives upside down in its shell with its head nearest the point of attachment. The plankton is then trapped in a layer of mucous and passed to the mouth by cilia.