The tube feet that are not busy pulling the urchin along appear to be engaged in a slow dance. The feet below look a little blurry, because they were moving when the picture was taken. Notice how long and thin they are. Tube feet not only help the urchin move, they also are used to grasp food, and they are part of the respiratory or breathing system.
The tube feet are part of the urchins water vascular system. They work like a hydraulic system. The urchin contracts its muscles to push water into the tube feet. This extends the feet outwards. When the muscles relax, the feet retract.
CJ Kazilek. (2009, December 23). Tube Feet. ASU - Ask A Biologist. Retrieved April 3, 2020 from https://askabiologist.asu.edu/fr/tube-feet
CJ Kazilek. "Tube Feet". ASU - Ask A Biologist. 23 December, 2009. https://askabiologist.asu.edu/fr/tube-feet
CJ Kazilek. "Tube Feet". ASU - Ask A Biologist. 23 Dec 2009. ASU - Ask A Biologist, Web. 3 Apr 2020. https://askabiologist.asu.edu/fr/tube-feet