What Is Inside a Sand Dollar?

Have you ever walked along the beach and found a sand dollar shell? This shell is called a test and is the endoskeleton of a sand dollar, a burrowing sea urchin. The shell is left behind when the sand dollar dies and its velvety spines fall off to reveal a smooth case underneath. The test may be white or grayish in color and has a distinct star-shaped marking in its center.

If you pick up the test and shake it gently, you may hear rattling inside. This is because the sand dollar's amazing eating apparatus is dried and loose within the shell. A sand dollar's body has five jaw sections, 50 calcified skeletal elements, and 60 muscles. A sand dollar extrudes these mouthparts to scrape and chew algae from rocks and other surfaces to eat, then retracts them back into its body. The dried-up bits that you hear when you shake the test are most likely remnants of the jaws.

Aristotle's Lantern and the Doves

The sand dollar has been the object of much attention spiritually, scientifically, and philosophically. The mouth of a sand dollar and other urchins is called Aristotle's lantern because the Greek philosopher and scientist Aristotle thought that it resembled a horn lantern, a five-sided lantern made of thin pieces of horn. The jaws, muscles, connective tissue, and teeth-like calcium plates of the skeleton make up Aristotle's lantern.

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Sand Dollar Facts

By Jennifer Kennedy

When a dead sand dollar is broken open, five v-shaped pieces are released, one from each section of the mouth. During a sand dollar's life, these parts function as teeth by allowing sand dollars to grind and chew their prey. When a sand dollar dies and dries up, its teeth become detached and closely resemble small, white birds that are often referred to as doves.

Many people have come to associate both the sand dollar itself and its doves as symbols of peace, which is why the doves are sometimes called "Doves of Peace." It is often said that releasing a sand dollar's doves releases peace into the world.

The Legend of the Sand Dollar

Shell shops often sell sand dollar tests with poems or plaques attached that tell the Legend of the Sand Dollar. The original author of the poem is unknown but the legend has been passed on for many years. Below is an excerpt of what is thought to be the original poem.

Now break the centre open
And here you will release,
The five white doves awaiting
To spread Good Will and Peace.

Christian authors have written many variations of this poem, likening sand dollar markings to the Easter lily, Star of Bethlehem, poinsettia, and the five wounds of the crucifixion. For some, discovering a sand dollar shell on the beach can lead to deep religious reflection.

Sources

• "Encyclopedia of the Aquatic World." Vol. 11, Marshall Cavendish, 2004.
• “Introduction to the Echinoidea.” Berkeley University of California UC Museum of Paleontology. 
• M., Chris. “Sand Dollars ARE Sea Urchins. Please Make a Note of It!” Sand Dollars ARE Sea Urchins. Please Make a Note of It!, 1 Jan. 1970.
• “The Echinoid Directory." Natural History Museum.