Ever stumbled upon a sand dollar at the beach or spotted one in a souvenir shop and wondered about its story? Far from the polished white disks many of us are familiar with, living sand dollars are a marvel of nature, boasting vibrant colors and a fascinating lifestyle beneath the sea.
Dead and dried, sand dollars are known for their bleached white appearance, showcasing a smooth exoskeleton adorned with a star or flower pattern. But alive? They’re a whole different spectacle. Sporting shades from reddish-brown to deep purple, these sea creatures are covered in tiny, flexible spines, not hair, which play a crucial role in their survival.
With 11 different types of sand dollars, let’s check out what their world is:
Belonging to the Echinoidea class within the Echinodermata phylum, sand dollars are close relatives of sea stars and sea urchins.
These ocean floor dwellers feast on microscopic algae and bacteria, contributing significantly to their marine ecosystems.
Despite lacking a brain, they possess a nerve ring that oversees bodily functions, showcasing nature’s incredible design.
With a ten-year lifespan, these creatures prefer company, sometimes living in densities as high as 625 per square yard! Their survival and reproduction strategies are as intriguing as their appearance, relying on the movement of their spines to feed and reproduce through the release of eggs and sperm into the ocean.
After death, the sand dollar leaves behind a skeleton, or “test,” prized by beachcombers worldwide. This calcium carbonate structure is beautiful and serves as a window into the sand dollar’s internal workings, including its unique feeding apparatus.
Alive, sand dollars play a pivotal role in their habitats, balancing invertebrate populations and serving as prey for select predators.
Their burrowing behavior aerates the ocean floor, promoting biodiversity. Yet, threats like overfishing and environmental changes pose significant risks to their populations.
Despite their commonality, the allure of finding a sand dollar remains unmatched. Often mistaken for ancient coins due to their shape and color, these sea creatures carry tales of mermaids and lost cities in folklore. Yet, their true value lies in the joy of discovering them, a sentiment echoed by guided shelling tours that offer a chance to uncover these treasures firsthand.
For those lucky enough to find a sand dollar, preserving it involves careful cleaning and possibly a bleach solution to whiten it. Sealing it with a glue mixture ensures its longevity, allowing you to keep a piece of the ocean’s mystery with you.
The sand dollar’s life is proof of nature’s wonders, from its unique feeding mechanisms to its role in the marine ecosystem. Whether it’s the age revealed by its shell’s rings or its ability to navigate ocean currents, every aspect of the sand dollar’s existence is a story waiting to be told.
In many places, it’s against the law to remove live sand dollars from their natural habitat, and for a good reason. These marine animals have a limited survival window outside their aquatic home, lasting only a few minutes. This is due to their unique respiratory system that utilizes petaloid, a series of holes acting as gills, from which tube-like feet extend to breathe.
The Echinarachnius parma, commonly known as the sand dollar, has garnered many nicknames due to its resemblance to dollar coins. In the United States, you also affectionately called them a sand cake, sea biscuit, or cake urchin. In New Zealand, terms like sea cookie and snapper biscuit look popular, while in South Africa, you often hear it called a pansy shell, highlighting its unique floral pattern.
Sand dollars have a fascinating approach to feeding. Some say they dine on a variety of small creatures and organic particles, including crustacean larvae, copepods, diatoms, and microscopic algae. Utilizing spines equipped with tiny, flexible cilia, they transport food along their bodies to their centrally located mouths.
Before consuming their prey, such as amphipods and crab larvae, they hold it in a “tiny, teepee-shaped cone of spines.” Their mouths contain a jaw with five teeth-like sections for grinding food—a process that can last up to 15 minutes, with digestion taking up to two days.
Those beautiful flower-like designs on a sand dollar? They’re not just for show. Known as lunules, these patterns consist of five sets of pores that process gas and water, creating a stunning design. These pores, along with the sand dollar’s oblong holes, act as a clever drainage system to prevent the creature from being swept away by waves. They also play a crucial role in gathering food.
Sand dollars have a unique way of anchoring themselves; they either stand upright, partially buried in the sand when the water is calm, or lie flat and burrow to avoid being tossed about by rough waves. They even increase their weight by growing heavier skeletons or ingesting sand.
With their hard skeletons and scarce edible parts, sand dollars don’t have to worry about predators too much. Yet, some marine animals, including ocean pout, California sheepheads, starry flounders, and large pink sea stars, do take on the challenge, making sand dollars prey even to their kind.
Just as tree rings tell the age of a tree, the growth rings on a sand dollar’s test reveal its age.
The larger the sand dollar, the more rings it has, indicating its age.
Monterey Bay Aquarium research shows that these marine creatures can enjoy a lifespan ranging from six to ten years, marking time with the increasing rings on their bodies.
Sand dollars are a testament to the ocean’s mysteries and the intricate web of life beneath its surface. By understanding and appreciating these enigmatic creatures, we can foster a deeper connection with the natural world and advocate for conserving marine habitats. The next time you hold a sand dollar, remember you’re holding a piece of the ocean’s history and a living creature that has survived millions of years through adaptation and resilience. Let’s protect these underwater treasures for future generations to marvel at and learn from.
