Sea stars belong to a group of backbone lacking invertebrates called echinodermata, which means “spiny skin”. Sea stars are fascinating animals with a crazy eating strategy! Sea stars begin by climbing on top of the prey using their tubed feet that function using a water vascular system. This means they take in water to their body through an opening called the madreporite and use water pressure to function their feet. If the sea star finds an animal with a hard exterior, such as a mussel, it can use this water pressure and tubed feet to open the prey exposing the soft interior. Some sea stars can apply 12 pounds of pressure when prying open prey!
Once the prey is opened or under the center of the sea star, the sea star excretes its stomach. The excretion of the stomach is referred to as eversion. With the everted stomach inside the prey’s protective covering it then begins to digest the soft tissues with digestive enzymes from the stomach. Even if the prey is a tightly sealed mussel as long as the sea star can find a tiny opening it can get its enzymes inside to devour its prey. Once the enzymes liquefy the meat of the prey it is then absorbed by the stomach tissue. The final digestion of nutrients is done inside the arms of the sea star by the organs called pyloric ceca. Once digestion is complete the stomach is then pulled back into the mouth and any hard parts of the prey are left behind.