Sand Dollars: Four Things You Didn't Know

The star-stamped bones of sand dollars are highly prized beach treasures, but few people know what the bottom-dwelling critters are like while they're alive. The truth is, they don't resemble what you'd discover in the sand after a high tide. At its peak, the sand dollar—also known as "sea biscuit" or "sand cake" in other regions of the world—is purple and hairy. It is a member of the Clypeasteroida group and may be found in tropical and temperate seas in the Northern Hemisphere. Here are nine facts you may not know about sand dollar shell, ranging from their various nicknames to the unique manner they eat.

1. When sand dollars are alive, they aren't white

The majority of people only see sand dollars after they've died. Their bones are the white "shells" found on the beach; while the marine species is alive, its color may range from a deep reddish-brown to a bright purple. Living sand dollars are coated in flexible bristles, known as spines, that obscure their star pattern, in contrast to the porcelain-like smoothness of their gift shop-popular skeletons. When it dies, the sun bleaches its skeleton (the "test"), rendering it white and fading the little spines.

2. Live Sand Dollars Cannot Survive Outside of Water for Long

Most jurisdictions make it unlawful to remove living sand dollars from the beach, although rules on dead species vary. If you're not sure if a sand dollar is living or dead, don't take it. They can only stay out of the water for a few minutes if they are alive. Sand dollars breathe with their distinctive "petals," which are a set of openings from which emerge tube-like, breathing feet.

3. They're Sea Urchins and Sea Stars' cousins

Sand dollars are burrowing invertebrates that belong to the echinoids, or spiny-skinned organisms, family of marine animals. They're called "irregular" sea urchins since they have a lot in common with their spherical counterparts in terms of structure.

They are also linked to radially symmetrical organisms such as sea lilies, sea cucumbers, and sea stars (called starfish), albeit the latter belongs to a distinct family.

4. They Have a Long List of Nicknames

"Eccentric sand dollar," or simply "sand dollar" in the United States, is the common name for the Echinarachnius parma species. Although it's also known as "sand cake," "sea biscuit," and "cake urchin," or "sea cookie" and "snapper biscuit" in New Zealand, the term stems from the animal's resemblance to dollar coins. It's known as a "pansy shell" in South Africa because of its flower-like design.