They function in movement, feeding and respiration. They contain no specialized excretory organs. Suction cups at the end of each tube foot attaches to the ground while the muscles contract to shorten the foot. These organisms eat by attaching their tube feet to the shells of the clam and wrap around it,holding it tightly. The clam's muscles fatigue allowing the shell to be pulled open.
Sea stars have a limited ability to regenerate.
A single arm cannot regenerate an entire body. They also typically have five arms, but these arms are slender and distinctly set off from the central disc. They move by means of their tube feet, with some assistance from their spines. They move chiefly by their spines. In crinoids, the body disc has a leathery skin containing calcareous plates.