Sand dollars are distinctive marine invertebrates, known for their unique flat, disc-like appearance and the delicate star-shaped pattern visible on their skeletal remains. These creatures are closely related to sea stars and sea urchins, belonging to the same group of spiny-skinned animals called echinoderms. Living primarily in shallow coastal waters, sand dollars typically inhabit sandy or muddy ocean floors where they often remain partially buried. Their flattened bodies are well-suited for burrowing, allowing them to navigate and find shelter within the seabed.
Survival Time Out of Water
A sand dollar’s survival outside of its aquatic environment is extremely limited, typically lasting only a few minutes. Once removed from the water, these marine animals face immediate challenges. Prolonged exposure to air rapidly leads to desiccation, which is the process of drying out. Their inability to breathe efficiently outside of water also contributes to their swift demise.
Why Sand Dollars Struggle on Land
Sand dollars cannot survive long on land due to several physiological adaptations that tie them intrinsically to their marine habitat. Respiration relies on a water vascular system and numerous tube feet, which facilitate gas exchange by absorbing oxygen dissolved in seawater. When out of water, these delicate structures collapse, preventing the sand dollar from obtaining necessary oxygen. Unlike fish, sand dollars do not possess gills; instead, oxygen diffuses directly through the walls of canals within their bodies.
Their bodies are also not equipped to retain moisture, causing rapid dehydration when exposed to air. Movement and structural support become impossible on land. Sand dollars use thousands of tiny, hair-like spines and cilia to move across the seabed and to burrow into the sand. Without the buoyancy and lubrication of water, these mechanisms are ineffective, and the animal cannot support its own weight or navigate. Their entire biological system is adapted for the stable, submerged conditions of the ocean floor.
Spotting a Live Sand Dollar
Distinguishing a live sand dollar from a dead one, often referred to as a “test” or skeleton, is straightforward. Live sand dollars typically exhibit a darker coloration, ranging from purplish-brown, reddish-brown, or gray, rather than the bleached white often seen in dried specimens. They are covered in a dense layer of short, fuzzy spines that give them a velvety texture. A clear indicator of life is the movement of these spines; if gently observed, they may be seen wiggling or shifting.
Another sign is the release of a harmless yellow substance called echinochrome if the sand dollar is handled. In contrast, a dead sand dollar will be smooth, rigid, and typically white or pale tan, having lost its spines and natural coloration due to sun exposure and decomposition.
Responsible Beachcombing
Responsible beachcombing practices are important for marine ecosystems. If you encounter a live sand dollar, gently return it to the ocean. Carefully place it back into the water, ideally below the low tide line or in the same area where it was found, allowing it to burrow back into the sand. Disturbing or removing live sand dollars from their natural habitat can cause them harm and is often prohibited by local regulations in many coastal areas.
Collecting only bleached white “tests” of sand dollars, their skeletons after the animal has died and decomposed, is generally acceptable. These empty shells no longer contain living tissue and are commonly sought as souvenirs. Leaving live marine organisms undisturbed helps maintain the delicate balance of the coastal environment, ensuring these unique creatures continue to contribute to the ecosystem.