Sand Dollars & Facts About Sand Dollars
Living in the southeastern United States, we have visited beaches along the Virginia, North Carolina, South Carolina, Georgia, Florida (Atlantic and Gulf side), and Alabama coast lines. I can tell you sand dollars are elusive creatures! We found them all over the beach on Jekyll Island, Georgia. Most of the photos in this post are from our visits.
Let’s take a close look at these fascinating creatures.
Facts About Sand Dollars
Do Sand Dollars Sting and Are Sand Dollars Dangerous?
While sand dollars do have spines, they are soft and do not pose any threat to humans beyond some minor scrapes.
However, living sand dollars emit a yellowish substance known as echinochrome, which is entirely harmless. We should always be cautious when handling live wild animals and be respectful of their well-being. Echinochrome is usually a sign that a sand dollar is stressed and would like to return to the water.
What Are Sand Dollars?
Sand dollars belong to the phylum Echinodermata, home to many sea creatures that display radial symmetry, such as starfish, brittle stars, and sea cucumbers.
The sand dollar taxonomy is as follows:
- Kingdom Animalia
- Phylum Echinodermata – radial symmetry sea creatures, including starfish, brittle stars, and sea cucumbers
- Class Echinoidea
- Order Clypeasteroida
- Family Clypeasteridae
- Genus Clypeaster
- Species Clypeaster subdepressus
There are around twenty different families within the order Clypeasteroida, amounting to over a hundred species total that are considered sand dollars. The main physical component that ties all of these species together is the flat appearance of their outer shell structure, called a test.
Sand Dollar Anatomy
The test or skeleton of sand dollars is made up of a combination of chitin, calcium carbonate, and silica. Their general shape is a spherical body made up of five symmetrical plates.
The symmetry of sand dollars is a unusual; adult bodies have a predominantly radially symmetrical shape, meaning the shape of their body is centered around a central axis point.
The symmetry of sand dollars is a unusual; adult bodies have a predominantly radially symmetrical shape, meaning the shape of their body is centered around a central axis point.
The bottom side of the sand dollars is called the oral side and the top side is called the aboral side. They have 40 bones and 60 muscles.
Age – Lifespan of Sand Dollars
Sand dollars typically live to be around 10 years old, and we can determine their age by the number of rings they have on their exoskeleton (similar to how we date trees.) The tests of sand dollars usually grow a new ring each year that they are alive so that the oldest sand dollar would have around ten rings on its exoskeleton.
Look at the photo above. How many rings do you count? To me it looks like 7-(ish!)
Where do Sand Dollars Live?
Sand dollar species can be found extensively throughout the globe. Typically, they stick to temperate or tropical climates and have been found on the coasts of the eastern United States to South Africa and even New Zealand.
They usually live in shallow waters just below the low line and like to live in mud-dense patches. However, they can be found just off the beach to fifty feet down.
What Do Sand Dollars Eat?
The mouth of the sand dollar is located in the middle of its underside. Tiny particles of food from the water or sand get trapped in the spines of the sand dollar and then are moved toward the mouth by small hairs called cilia. Did you know that cilia means eyelashes in Latin?
When the waters are calm, sand dollars will orient themselves upright and bury themselves halfway out of the sand. They can easily catch tiny, free-floating organisms such as larvae, algae, and diatoms in this position. Sand dollars are omnivorous.
A sand dollar’s mouth is on the bottom side of their body, and their anus is on the top side. Below are close-up photos of the mouth area. The also have an upper and lower esophagus and a stomach. Just like in humans, there are enzymes in the stomach of a sand dollar to help break down food. Whatever isn’t used by the sand dollar is excreted through the anus. It can take up to two days for food digest.
But, if waters become choppy, sand dollars will lay themselves flat and bury themselves if need be. While flat or buried, sand dollars will use their spines and cilia on their bottom halves to capture and ingest edible debris beneath them.
Do Sand Dollars Have Teeth?
Yes, sand dollars do have mouth parts that resemble and work like teeth. Pictured below are the five mouth parts we retrieved from a sand dollar we found over 15 years ago. For the sake of this sand dollar study, we did crack open this one.
As larvae, sand dollars depend almost exclusively on microscopic plankton to sustain themselves until they grow into adulthood.
How Do Sand Dollars Move?
Sand dollars have spines that help them move through the sand. The spines dry up and fall off after the sand dollar dies. In the photo below, you can see the trail left behind by the sand dollar as it slowly moves along the shore.
How Do Sand Dollars Reproduce?
Sand dollars participate in a unique form of reproduction known as broadcast spawning. Sand dollars often live in giant colonies, with over 600 individuals in one congregation. These 600+ sand dollars may occupy less than one square yard!
When they are ready to mate, the males and females will release their respective gametes in the water, with males and females able to produce hundreds of thousands of eggs and sperm per year.
The gametes freely mingle and combine into zygotes, eventually becoming embryonic sand dollars that float throughout the ocean’s currents as they develop.
It takes around three months for a sand dollar to fully mature.
While the adults only reproduce sexually, it has been observed that larval sand dollars can clone themselves. This usually occurs when food and temperatures are optimal or when the larvae are near a predator. In the latter instance, they will clone themselves in an attempt to survive and distract the predator.
Once the larvae have developed long enough, they anchor themselves to the seafloor and undergo metamorphosis, resulting in a juvenile stage. In this stage, they remain on the seafloor to collect larger quantities of food, and juveniles who live in strong currents will ingest sand to weigh down their bodies.
Are Sand Dollars Endangered?
Sand dollars are not considered endangered species but are all threatened by many anthropogenic issues.
All stages of sand dollar development are considered necessary for the diets of many other marine species, with their biggest predators being fish, sea stars, crabs, and other marine life that consume tiny larvae. Direct threats to the well-being of sand dollars include industrial fishing, bottom trawling, and direct harvesting by divers for aesthetic purposes. Other threats include the overall pollution of the oceans.
Other Fun Facts About Sand Dollars
- The nickname “sand dollar” derives from the fact that the bleached skeletons of these echinoderms resemble older, much larger versions of American and Spanish coinage
- Calcium carbonate, the same material that makes up the test of sand dollars, is also the main ingredient in many antacids taken to help upset stomachs. Not to worry, though, the calcium carbonate used by humans is not made from crushed-up sand dollars!
- The sand dollar’s scientific name is Mellita Quinquiesperforata.
- Humans and most other mammals have bilateral symmetry.
- Radial symmetry is more commonly found in plants than in animals, but besides echinoderms, the other phylum of radially symmetrical animals are the cnidarians (Jellyfish, corals, and anemones)
- Some animals, such as sea sponges, have no symmetry at all; this is called asymmetry
- Just like sand dollars, many eukaryotic cells have cilia to aid them in locomotion and moving water around its membrane. These cilia are considered membrane-bound organelles which extend through the cell membrane
- While sand dollars do have spines, they are soft and do not pose any threat to humans beyond some minor scrapes. However, living sand dollars emit a yellowish substance known as echinochrome, which is entirely harmless. However, one should always be cautious when handling live wild animals and be respectful of their well-being. Echinochrome is usually a sign that a sand dollar is stressed and would like to return to the water
Other Resources to Go with a Sand Dollar Study
