starfish

It's easy to see how the starfish got its name—with their pointed arms, these creatures look like stars fallen to the ocean floor. But starfish aren't fish at all. Fish are vertebrates, animals with backbones. Starfish, like their close relatives sand dollars and sea lilies, are invertebrates, animals without backbones. It's no wonder scientists prefer to call them "sea stars."

Image credits: main image: courtesy of Gerald and Buff Corsi, California Academy of Sciences.