Starfish exhibit a fivefold radial symmetry, unlike the bilateral symmetry seen in most animals. This symmetry means they can be divided into five identical segments radiating from a central point.

Bonnie Hao | Beijing, China Scientists can’t pinpoint exactly why starfish evolved to have radial symmetry, with arms—usually five, but as many as 40 in some species—growing from a central axis.

Starfish, or sea stars, belong to a group called echinoderms, which also includes sea urchins and sand dollars. They’re famous for their five-pointed symmetry, but their real magic lies in their ...