The Many Names of Clypeasteroida

By Alex Scott

different types of sand dollars

If you ask a beachcomber in New Zealand what they call the flat animal with a five-pointed pattern that often washes up onshore, they will say sea cookie or snapper biscuit. If you ask a South African, they will say pansy shell; a Latin American would say galleta de mar, also meaning sea cookie; and in other places, you might hear sand cake, cake urchin, sea biscuit, or sand dollar. This sea urchin, belonging to the order Clypeasteroida, has received many names, but, no matter what you call it, is a prize to beachcombers all around the world.

sand dollar on florida beach

Jennifer Lonoff Schiff (Florida)

The sand dollar (perhaps its most common name in the U.S.) is a member of the phylum Echinodermata, which also includes sea stars, sea cucumbers, and other sea urchins. The first sand dollar evolved during the late Jurassic era, with more modern species appearing in the Eocene epoch (56 to 34 million years ago).

living sand dollars

Left to right: Sharmon Simonetti (Florida), Trudi Flaherty (California), Sara Robinson (California)

Sand dollars are found in shallower sandy areas close to the shore around the world, from latitudes up to Alaska down to the southern tip of South Africa. Every continent has its own species of sand dollars, each with its own color and size and, as stated above, a unique moniker.

sand dollar tests

Left to right: Jaime Sawczyn (Florida), Kristina Braga, Jennifer Lonoff Schiff

The sand dollar’s most defining trait, and the source for many of its various names, is its “test” or circular skeleton, measuring 3 to 4 inches in diameter, that has a five-pointed pattern on its dorsal side. These five “petals” are actually pores that take in water and oxygen for respiration. Some species of sand dollar also have holes in their tests called lunules, which allow water to pass through the sand dollar while it remains safe buried in the sand on the ocean floor. Some young sand dollars will even ingest sand to weigh themselves down in rough tides.

beach with sand dollars

Left to right: Scott Smith (Maine), Sharmon Simonetti (Florida)

The animal’s skin is covered with tiny spines and even smaller hairs called cilia. The sand dollar uses cilia to move across and burrow into the sand—as well as to catch food that floats by and transport it to their mouth, which is located on their underside and has five large teeth-like structures. Sand dollars feed on larvae, algae, and other small organic material found in shallow waters. They can also “stand” upright in calm waters to maximize the surface area available for catching food.

sand dollar on beach in Maine

Scott Smith (Maine)

Sand dollars generally live together in large groups and, like most urchins, reproduce by external fertilization, meaning males and females expel gametes into the surrounding water where fertilization occurs. Because groups are generally closely packed together, the chances of fertilization through this method are high. Some sand dollar larvae are also capable of asexual reproduction. The larvae of the eccentric sand dollar (Dendraster excentricus), found along the Pacifc coast of North America, can detect mucus from a predatory fish and can split itself in two, giving it a higher chance of one surviving while also becoming smaller in size to avoid detection. A sand dollar can live for up to ten years, and like trees, scientists can tell the age of a sand dollar by counting the rings on its test.

sand dollar and sea biscuit

Left to right: Jaime Sawczyn (Florida), Barbara Smith (Florida)

In the past, sand dollars were often thought to be coins used by mermaids or citizens of Atlantis, but that isn’t the only legend surrounding the sand dollar. According to some Christians, the test of a sand dollar represents many symbols of the story of Jesus Christ. The five-pointed pattern on the top and bottom of the test represent the Christmas poinsettia and the Easter lily, while the five lunules represent the five wounds when Jesus was crucified. And when a sand dollar test is broken open, the five teeth-like structures resemble white doves that symbolize the peace and joy of Christmas.

beach sand dollar

Left to right: Ryan Headley (Virginia),  Scott Smith (Maine),  Lisa Foy (Florida)

It is important for beachcombers to be able to distinguish a live sand dollar from a dead one, so that they don’t accidentally bring home a live animal. The easiest way to tell is to look for a colorful top and spines along the edge of the sand dollar. Live sand dollars come in various colors, from red to blue to purple, but once they die, their test is exposed and the sand dollar looks tan, gray, or white. Also, visible spines along the edge of the test mean the animal is still alive, even if they aren’t moving. Sand dollars are not an endangered group of animals, but they are threatened in various parts of the world due to trawling, pollution, and over-collection by beachgoers. Make sure there are no spines and no color on a sand dollar test before you pick it up!

This article appeared in the Beachcombing Magazine September/October 2021 issue.

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1 comment

Do you buy rare shells junoia, cowie, white tooth, conus,etc100 shells I want to sell.

Bill Roberts April 04, 2023

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