What is sea stars unique characteristic?

Sea stars can regenerate (can grow any part as long as the central disk is still partially in tact), has skin containing calcium carbonate for protection, can see light and dark (thanks to eyespots on each arm), to eat it puts its stomach into a mussel or clam shell to digest then slurp up, tube feet with strong suction to help eat clams and mussels, and pedicellaria (microscopic pinchers on skin) to keep clean, water vascular system (aids gas exchange, digestion, movement, and movement of flud throughout the body).