common sea stars are unpopular with mollusc fishermen, because they can eat up to 10 molluscs in 24 hours. A sea star captures its prey with the hundreds of suction feet, called ambulacral feet, covering its arms. It forces the two halves of the shell apart and then inserts its stomach. Once it has digested the mollusc it sucks the food and its stomach back inside itself. These sea stars move very slowly, covering no more than a kilometre in their entire lifetimes.