Starfish walking on the beach

Although sea stars live underwater and are commonly called "starfish," they are not true fish. They do not have gills, scales, or fins like fish do.

Sea stars also move quite differently from fish. While fish propel themselves with their tails, sea stars have tiny tube feet to help them move along.

Because they are not classified as fish, scientists prefer to call starfish "sea stars."
Sea stars belong to the phylum Echinodermata. That means they are related to sand dollars, sea urchins, sea cucumbers, and sea lilies. Overall, this phylum contains approximately 7,000 species.1

Many echinoderms exhibit radial symmetry, meaning their body parts are arranged around a central axis. Many sea stars have five-point radial symmetry because their body has five sections. This means that they do not have an obvious left and right half, only a top side and a bottom side. Echinoderms also usually have spines, which are less pronounced in sea stars than they are in other organisms such as sea urchins.