A sand dollar is a type of marine invertebrate, specifically a flattened, burrowing sea urchin. These creatures belong to the order Clypeasteroida, making them relatives of sea stars and other sea urchins. When found washed ashore, their dried, disk-shaped skeletons are often a common sight for beachcombers. This unique appearance has led to their distinctive common name, reflecting both their visual qualities and preferred habitat.
The Dollar Connection
The “dollar” in “sand dollar” references the appearance of their rigid skeletons, called tests, found on beaches. These tests are typically circular and flattened, resembling a large, silvery coin. Historically, this likeness was drawn to the old Spanish dollar (38-40 mm diameter).
When alive, sand dollars are covered in tiny spines, but once they die and wash ashore, these spines fall off, and the sun bleaches their tests white or grayish-white. This process reveals a distinct five-part, often star-shaped or flower-like, pattern on their surface, further enhancing their coin-like appeal. Adult sand dollars typically measure between 2 to 4 inches (5 to 10 cm) in diameter, a size comparable to many larger coins.
The Sand Connection
The “sand” in the name refers to their natural environment and behavior. These marine animals primarily inhabit sandy seafloors in shallow coastal waters, though some species can be found in deeper ocean habitats. Live sand dollars are not white; their natural coloration varies (brown, gray, purple, or reddish-brown), providing camouflage with the sandy bottom and protection from predators.
They possess thousands of tiny, velvet-like spines and hair-like cilia. These structures are instrumental in their movement, allowing them to creep across the seabed and burrow efficiently into the sand. They can bury themselves quickly (sometimes in 10 minutes), finding shelter and food within the sediment.
Other Names and Legends
Beyond “sand dollar,” they are known by various other common names globally, reflecting diverse perceptions. Alternative names include “sea cookies,” “snapper biscuits,” “pansy shells,” “sand cakes,” and “cake urchins,” often alluding to their flat, rounded shape or texture.
Folkloric explanations also contribute to the understanding of their naming. Some legends suggest sand dollars represent coins lost by mermaids or even tokens from the mythical city of Atlantis. In Christian symbolism, their features are interpreted to represent elements of Christ’s story: the star pattern symbolizes the Star of Bethlehem, and five holes represent Christ’s wounds. Breaking open a sand dollar may reveal five tooth-like structures, which some interpret as tiny doves, symbolizing peace.