猜猜"sand dollars"是什麼？

猜猜"sand dollars"是什麼？
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Or that I knew the most tedious job in the house was wiping down a ledge in the bathroom where seashells and sand dollars were perched.

---Reader's Digest April, 2006

Sand dollars are flat circular sea animals. They are from the class of marine animals known as Echinoids, spiny skinned creatures.

更詳盡的資料：
http://www.gma.org/Tidings/sanddollar.html