Some echinoderms eat by everting their stomachs over their prey and digesting them externally; whereas others use modified parts of their skeleton as teeth, tentacles or tube feet to direct food to their mouth opening. Echinoderms are sea animals that ingest nutrition in a variety of ways.
Echinoderms such as sea cucumbers use tiny tentacles around their mouths to suck in mud from the sea floor and extract bits of food from it. Sea lilies and feather stars trap plankton by using the tube feet on their outspread arms. They guide the plankton to their mouths, which sit on top of the body. This is different from other echinoderms, whose mouths tend to be on the underside of the body.
Many starfish are predatory, and if their prey is small enough, they will swallow it whole. Some starfish will swallow prey that's very large, even if it means having to break their mouth parts to do so. Other kinds of starfish externally digest the prey. When this type of starfish captures a bivalve, such as a mussel or a clam, it will use its tube feet to slowly pull the shells apart and then insert its stomach inside the bivalve. It then digests the inside of the bivalve.
Sea urchins graze on algae and small animals such as barnacles and worms using an arrangement of teeth that are self-sharpening and can even chew through rock.