A sand dollar is a type of flattened, burrowing sea urchin, belonging to the class Echinoidea. These marine animals are invertebrates, related to sea stars and sea cucumbers. The question of whether they are rare depends on where and in what condition one is searching for them. The object most people recognize is actually the calcium carbonate skeleton, or test, of the animal, not the living creature itself. Understanding this difference is the key to determining the likelihood of a find.
Defining Rarity: Live Versus Skeleton
Finding a living sand dollar is uncommon. Live sand dollars are typically found in the subtidal zone, residing below the mean low tide line, partially or completely buried in the sand. When alive, the creature is covered in a dense layer of tiny, movable spines, giving it a dark, velvety appearance that can range from brown, gray, purple, or violet. These spines are used for locomotion, burrowing, and moving food particles toward the central mouth.
In contrast, the familiar white object found on beaches is the dead skeleton, or test, of the animal. After the sand dollar dies, the soft tissues and spines disintegrate and fall away, leaving behind the hard, brittle, and smooth internal shell. The test is then bleached white or pale beige by the sun and surf. These bleached tests are frequently washed ashore in large numbers, particularly after storms or during periods of heavy current, making them common finds on certain coastlines.
Essential Sand Dollar Habitats
Sand dollars thrive in specific marine environments. They are most commonly found on sandy or muddy seafloors in shallow, temperate, and tropical waters worldwide. These invertebrates are deposit feeders, relying on fine-grain sand that allows them to burrow while accessing food particles and detritus.
While juveniles are sometimes found closer to the shore in the intertidal zone, adults often move to greater depths. Many species live in the subtidal zone, ranging from just below the low tide line to about 100 feet deep. They often congregate in large groups, or “beds,” positioning themselves vertically in the sand to maximize the capture of plankton.
Ethical Collection Guidelines
It is important to determine the condition of any specimen before collecting it. Removing a live sand dollar from the water is prohibited in many coastal regions and can disrupt the marine ecosystem. A specimen that is dark in color and covered in a velvety coating of fine, hair-like spines is almost certainly still alive and should be left undisturbed.
A reliable way to check for life is by performing an observation test. If you hold the specimen, a living sand dollar’s spines will exhibit slow, coordinated movement. Another indicator of life is a harmless yellow-tinted substance, called echinochrome, which a live specimen may leave on the skin. If any of these signs of life are present, the sand dollar should be returned to the water immediately, ideally in an area with calm currents. Only the white, smooth, and brittle skeletal tests should be taken from the beach.