a flat type of sea urchin (= a small sea creature with a round shell covered with sharp points) that lives partly in sand below the surface of the water. The outer skeletons (= the bony frame supporting the body) of dead sand dollars are often found on beaches.

Sand dollars are marine creatures that are roughly the size of the palm of your hand. 沙钱是一种海洋生物，大约有手掌大小。

She spent a carefree hour on the beach searching for sand dollars. 她在海滩上无忧无虑地玩了一个小时，寻找沙钱。