Both have their mouths (oral surface) at the bottom of their bodies. However, a sea urchin has teeth called aristotles lantern that scrapes algae off rocks, while a sea star ejects it stomach around...
Yes they are. They are both echinoderms
Because they both have mouths and digestively similar
A sea star is called a sea star simply because of where it lives (the sea) and what it looks like (a star), simple!
both of them live in the ocean every where and they are echinoderms