Sand dollars are fascinating creatures found on sandy beaches. Their flat, round shape and unique characteristics make them popular among beachgoers.
But beyond their beauty, sand dollars are important members of marine ecosystems. Sand Dollar Alive keeps the ocean environment balanced and healthy. In this article, we’ll explore 7 facts about sand dollars and explain why protecting them from harm is important.
What Are Sand Dollars?
Sand dollars are a type of echinoderm of phylum invertebrates, which is the same group of animals that includes sea stars, sea urchins, and sea cucumbers. Sand dollar classification falls under the family Clypeasteridae of the marine echinoids class. Sand Dollar has 250 species and sizes 5 to 10 cm.
What color are sand dollars? living sand dollars come in different colors like super purple-brown, and reddish brown and if you see from a distance in water looks blackish.
Living sand dollars are covered with bristles spines when touched by these moving hair structures, it feel fuzzy, these spines hide the beautiful star-shaped pattern on the sand dollar body present on the back side, this pattern looks like 5 petals of a flower( look at image) and is called petaloid ambulacra.
These flower petals, like holes or pores, help in seawater, which has dissolved oxygen and nutrient-rich materials inside the body. When a sand dollar dies and is bleached by the sun, these spines fall off, leaving the sand dollar a hard, flat skeleton called a “test.”
If you see sand dollars piles on the beach and think what are sand dollars made of? Let me explain to you sand dollar exoskeleton is made of plates of calcium carbonate CaC03 and the muscles that pack them.. Sand dollars live in sandy, shallow waters along the coast and are most commonly found at depths of 3 to 40 meters (10 to 130 feet). They weigh less than 1 ounce and survive 8 to 10 years depending on the environment.
Despite their name, sand dollars aren’t actual coins, they are called sand dollars because in ancient times they looked similar to American and Mexican dollars. In the Bahamas, they are still called the sand dollar as currency. Their circular shape and distinct pattern basically are rings marine scientists say these rings on dried sand dollar upper body show age same as growth rings of plants indicate their age.
7 Cool Facts About Sand Dollars
Here are 7 interesting facts about sand dollars, including some biological details and statistics:
1. What’s Inside a Sand Dollar?
Inside a sand dollar, you’ll find a mouth, digestive system including(the esophagus, singular intestine, stomach, pharynx, and anus), reproductive organs, and nerve ring as well as tiny tube feet that help them catch food and move.
As mentioned above sand dollars have spines that are also used for moving food particles into their body through their mouths called Aristotle lanterns a group of 5 teeth-like sections also called sand dollar doves arranged in a symmetric shape packed with 50 calcium-made elements along 60 muscles that are present inside their body, sand dollar mouth is present at the central underside of its body.
These internal teeth are used for grinding food particles, this grinding takes 15 minutes of food before swallowing, and the sand dollar digestion process takes around 48 hours. If you are thinking, what do sand dollars eat then let me explain to you they feed on tiny organic fragments particles as well as algae, plankton, crustacean larvae, copepods, detritus, and diatoms.
A study shows that sand dollars can consume up to 3-5% of their body weight in food each day. According to the Monterey Bay Aquarium sand dollar flexible spines and pincers (pedicellariae) have mucus coating that traps tiny amphipods and tiny crab-floating larvae sand dollars are not only used spines for trapping food but are also used for movement across the sandy surface and as gills for respiration..
As mentioned earlier The sand dollar’s mouth is located on the bottom of its body, where it filters food from the water and its anus is present at the posterior edge.. Sand dollars have no eyes, but they can sense light and the movement of nearby objects using specialized cells called photoreceptor cells.
These cells are located in the spines and tube feet of the sand dollar. Since sand dollars have NO BRAIN, many body functions of their body are controlled by their nerve ring. When sand dollar dries and dies all the internal organs are dried, so if you ever find a bleached sand dollar on the beach, upon shaking you hear a rattling sound, these are sand dollar dried organs inside.
Catching sand dollars live state is prohibited because they can’t survive out of water for a few minutes, people ask me are sand dollars are dangerous sand dollars poisonous if we touch them, so let me tell you they are not dangerous for us, they are innocent creatures, don’t touch living sand dollars unnecessarily because this checking can hurt them.
2. Sand Dollar Feet
If you’ve ever seen a sea star, it usually has five arms that help it move and find food. Sand dollars are close relatives of sea stars, but they don’t have arms. Instead, they have a round, flat body with five-part symmetry, and adult sand dollars are usually 5 to 10 cm wide.
When a sand dollar is alive, it is covered in brown spines. These spines help the sand dollar creep along the sand, hide for protection, and search for food. Over time, these spines are no longer used for long-distance movement but are great for slow crawling.
Sand dollars move mostly with their tube feet, which look like tiny hairs on the bottom of their body. These tube feet work with a special system called the water vascular system, which uses water to help the sand dollar move. The spines also help with small movements. The tube feet are important not only for movement but also for catching tiny food particles from the water.
Sand dollars have hundreds of tube feet, which are also helpful for digging into the sand to hide from predators. If you ever find a live sand dollar on the beach, you might feel the tiny hair-like structures on its surface, called cilia. Make sure to put it back in the water immediately to survive. Also, wash your hands before touching one, as dirty or oily hands can harm these gentle creatures.
Looking for a guide about How to Clean Sand Dollars? check out our guide and clean your sand dollar shells effectively at your home.
3. Sand Dollar Mouth
The mouth of a sand dollar is located at the center of the underside of its body and is a key part of its feeding system. The anus is located near the edge on the bottom of its body.
The sand dollar’s mouth contains a specialized feeding structure called Aristotle’s lantern, which has five jaw sections used for scraping, grinding, and chewing food.
The grooves on a sand dollar, called ambulacral grooves, extend from the center of the underside toward the edges. These grooves help transport food particles collected by the sand dollar’s spines and tube feet. However, sand dollars do not scrape algae from rocks, as they are not equipped to do so. Instead, they feed on tiny organic particles, plankton, detritus, and algae suspended in the water or settled on sandy surfaces. Their tube feet and spines guide these particles to their mouth.
When sand dollars feed, their tube feet on the underside help push food into the mouth. The feeding process is gentle and efficient. Live sand dollars often have spines and tube feet covered in mucus to trap small prey, such as crustacean larvae or tiny amphipods, which can be seen getting caught on the underside of the sand dollar.
I live near 9805 N Ocean Shore Blvd, Palm Coast, FL 32137, and whenever I go scuba diving in August, I often see an abundance of sand dollars on the ocean floor. It’s fascinating to watch them trap tiny creatures on their underside.
4. Who Eats Sand Dollars?
Sand dollars have a hard, protective skeleton called a test, made primarily of calcium carbonate (CaCO3). Despite this rigid structure, they still face threats from predators. The main predators of sand dollars include sea stars, such as the bat star and ochre sea star, and some other kinds of seastars, we have seen in California eating alive sand dollars, interestingly, they prey to open the test to feed on the soft tissues inside.
Other common predators are crabs, lobsters, and fish, including eels, California sheepshead, and starry flounders. Large sea stars, such as the pink sea star, are also known to attack sand dollars. In addition to these marine predators, shorebirds, like sanderlings and seagulls, often prey on sand dollars when they are exposed during low tide. These birds peck at the tests to reach the soft tissue inside.
While the hard skeleton provides some defense, it is not impervious to the strength of predators like sea stars, which use their tube feet and hydraulic pressure to force open the test. Additionally, sand dollars rely on burrowing into the sand as a primary method of avoiding predation. They can partially or completely bury themselves, making it harder for predators to detect them.
Interestingly, younger sand dollars have been observed to ingest sand grains to increase their weight and prevent being washed away by strong currents or waves, which also helps them remain hidden from predators. This behavior highlights their adaptation to living in sandy and dynamic environments.
Although sand dollars face many threats, their ability to blend into their environment and their unique defensive adaptations, such as burrowing and reinforcing their skeleton with sand, help them survive in predator-rich habitats.
In Japan, it is safe to eat sand dollars. They are offered at restaurants. Once in Kyoto Japan, I was with my Japanese marine chief Eng Sushi Kanat we ate sand dollars fleshy parts just dipping them in soy sauce and other seafood dips. Interestingly it was delicious.
5. Sand Dollars Living Spaces Are Crowded
Sand dollars usually live in large groups on the ocean floor, often partially buried in the sand. In one square meter, there can be as many as 625 sand dollars.
They reproduce through a process called broadcast spawning, where males and females release their eggs and sperm into the water at the same time. This increases the chances of fertilization, as hundreds of thousands of eggs can be released during their breeding season, which happens between July and August. The life cycle of a sand dollar is very complex, very less they reach the adult stage.
Living in groups also helps young sand dollars find good places to grow. Pacific sand dollars (Dendraster excentricus) can grow up to 9 cm wide and live for about 10 years. They reproduce by releasing 356,000 to 379,000 eggs at a time, and the larvae hatch in about 28 hours. Sand dollars eat algae and plankton, which they filter using small tube feet and spines. This helps recycle nutrients in their environment.
6. How Are Sand Dollars Born?
At Mote Marine Laboratory & Aquarium in Sarasota, Florida, we observed how sand dollars reproduce during a live virtual event. Using a microscope, we watched the fertilization process, which took about 30 minutes. This showed us how sand dollars have fascinating ways of reproducing and their importance in the ecosystem.
Sand dollars use a method called broadcast spawning, similar to corals and some fish. Females release 356,000 to 379,000 eggs, while males release sperm into the water. This creates billions of reproductive cells (gametes), but only about 1% of the fertilized eggs survive to become adults because of predators and environmental challenges.
The eggs hatch into larvae in about 28 hours, and it takes around three weeks for these larvae to grow into young sand dollars. They become adults capable of reproducing at about four years old and can live up to 10 years. Sand dollars are most active in reproducing during spring and summer, influenced by factors like water temperature, sunlight, and the phases of the moon.
7. Fun Facts for Kids about Sand Dollars
1. What’s in the Name of a Sand Dollar?
Sand dollars aren’t actual money, but sailors once called them “mermaid coins,” thinking they were magical treasures from the sea!
2. Not Always White!
The sand dollars you find on beaches are white because they’re just the skeletons of dead sand dollars. When alive, they are purple, brown, or even greenish and covered in tiny spines that make them look fuzzy!
3. Built Like a Star!
If you look closely, the pattern on a sand dollar’s top looks like a flower or a star. This design comes from their internal skeleton, called a *test.*
4. Slow Movers
Sand dollars don’t swim—they use their spines like little legs to crawl slowly across the sea floor.
5. Underwater Filters
They’re like tiny underwater vacuum cleaners, sucking up microscopic food like plankton with hair-like cilia.
6. Ocean Architects
When sand dollars group together, they can help keep the sandy sea floor stable. Scientists call them “ecosystem engineers!”
7. How Old Are They?
Sand dollars can live for 6–10 years. You can count the growth rings on their skeletons to figure out their age.
8. Survival Tricks
Baby sand dollars sometimes swallow heavy sand grains to weigh themselves down, so they don’t get carried away by waves!
9. Starfish Relatives
Sand dollars are cousins of starfish and sea urchins. All of them belong to a group of animals called echinoderms, which means “spiny skin.”
10. Sand Dollar Doves
When a sand dollar breaks apart, you might find tiny white pieces inside that look like doves. These are actually parts of its skeleton!
11. Hidden Mouths
A sand dollar’s mouth is called “Aristotle’s lantern” because it has five tiny teeth inside that grind up food. It can take two days to digest one meal!
Fun Activity!
Next time you’re at the beach, try flipping over a sand dollar and watch it move its tiny spines. But remember, if it’s alive, let it stay in the ocean where it belongs!
Why Collecting Alive Sand dollar Prohibited
Collecting living sand dollars for decoration is illegal in many states, including South Carolina, where the fine can reach $500. Florida and Georgia have similar regulations, with enforcement often left to local municipalities. This practice is not only against the law but is also considered cruel to marine life. Vacationers should be aware of these laws to avoid penalties and protect marine ecosystems.
Frequently Asked Questions
What’s Inside a Sand Dollar?
Inside a sand dollar, you’ll find its mouth, digestive system, and tiny tube feet that help it move and eat. The skeleton, called a “test,” protects these internal organs.
How Do Sand Dollars Move?
Sand dollars use their tube feet to glide across the sea floor. They can bury themselves in the sand to avoid predators.
Are Sand Dollars Alive When They’re Washed Up?
If a sand dollar is washed up on the shore, it is usually dead. Living sand dollars are typically buried in the sand to feed and rest.
What Eats Sand Dollars?
Sand dollars are preyed upon by sea stars, crabs, lobsters, fish, and birds. These predators are part of the ocean’s food chain and help regulate the sand dollar population.
How Are Sand Dollars Born?
Sand dollars reproduce by releasing eggs and sperm into the water. The fertilized eggs develop into larvae, which float in the water until they settle on the ocean floor and grow into adult sand dollars.
Conclusion
I explained the 7 interesting facts about sand dollars, in detail along with how important creatures they are in the ocean. By understanding more about their biology and role in the environment, we can appreciate these creatures even more.
Remember, it’s important to respect sand dollars and not harm them by taking live ones from the wild. If you have any queries about marine life, you can ask in the comment box below, we would love to reply to you shortly. Thank You…..
