Sandkjerner

Sandkjerner, commonly known as sand dollars, are small, flat, and disc-shaped echinoids belonging to the family Mylodactylidae. They are often found buried in sandy ocean floors, particularly in shallow waters along coastlines. Unlike their close relatives, sea urchins, sand dollars have a more flattened body structure, resembling a dollar coin, which gives them their name.

Sandkjerner are typically found in temperate and tropical coastal regions worldwide, thriving in sandy substrates. They play a crucial role in marine ecosystems by aerating the sediment through their feeding process, which helps maintain healthy seafloor habitats. Their diet primarily consists of organic matter, plankton, and detritus, which they filter from the sand using specialized tube feet.

These echinoids have a distinctive five-part symmetry, though their skeletal structure, known as a test, is often obscured by a covering of fine, white spines when alive. When sand dollars die, these spines fall off, leaving behind a flat, star-shaped pattern that resembles a flower or a dollar coin, which is how they are often identified in fossilized form. Fossilized sand dollars are sometimes found in sedimentary rock layers, providing insights into ancient marine environments.

Sandkjerner are not typically considered edible by humans, though some cultures historically consumed them as a delicacy. They are primarily of interest to marine biologists, fossil collectors, and beachcombers. Due to their ecological importance and sensitivity to environmental changes, they serve as indicators of the health of coastal marine ecosystems. Conservation efforts often focus on protecting their habitats from pollution, overfishing, and habitat destruction.