A sand dollar is a flat, round sea creature related to sea urchins and starfish. When alive, sand dollars are covered in tiny, velvety spines and usually have a purple or reddish-brown color. They live on sandy ocean floors, moving slowly as they eat tiny particles of food from the sand.

Most people encounter sand dollars as white, bleached skeletons washed up on beaches. These delicate discs have a distinctive five-petal pattern on top that looks like a flower. The pattern is actually where tube feet once poked through when the animal was alive, helping it breathe and move. If you find one intact, you're lucky: they're fragile and break easily in the waves.

Beachcombers love finding them because they're beautiful and relatively rare. Some people consider them good luck.

If you shake a dried sand dollar, you might hear rattling inside. Those are pieces of the animal's internal structure, called doves, that have broken loose. According to beach legend, these five pieces represent doves of peace, though they're actually parts of the sand dollar's jaw structure that helped it eat.