Sand Dollar skeletons make popular collection items for seashell collectors.
Sand Dollar Scientific Classification
Sand Dollar Conservation Status
Sand Dollar Facts
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It can be the highlight of your seashell collecting trip to find a bright white Sand Dollar at the beach.
The skeletons of these animals are popular with collectors. When they are alive, Sand Dollars actually have gray or purple spines and fine hairs covering their bodies. They move along the sea floor and bury themselves in the sand. When they wash onto the shore, they are usually dead and make great additions to a seashell collection.
Sand Dollar Facts
- The larvae form of Sand Dollars can clone themselves and continue to grow and develop as two distinct animals.
- There are 250 or more species within the Sand Dollar order, Clypeasteroida.
- Most species of Sand Dollars move along the ocean floor using their spines and cilia.
- A few species of fish, including Cod and Flounder, eat Sand Dollars. These fish can even get through the hard skeleton of the Sand Dollar.
- While Sand Dollars are not endangered, collecting live specimens is illegal in most areas. This is to help preserve and protect their natural habitat and the ecosystem there.
Classification and Scientific Name
The well-known sand dollar is actually an entire scientific order, known as Clypeasteroida. There are at least 250 species that belong to multiple suborders and families. Many share similarities, but color, size, and location can all vary.
They are part of the superorder Gnathostomata. This includes other sea urchins that are all irregularly shaped and have a central mouth on their underside. The class Echinoidea includes all sea urchins, over 900 species total. Most have round shells with hard spines all over them. Most sea urchins eat algae and are very useful in aquariums to keep the algae growth in check.
Sand dollars are part of the phylum Echinodermata. Members of this phylum are known as Echinoderms. This translates to “echino-,” which means hedgehog, and “-derm,” which means skin. While not all members of the phylum have spikes or spines like sea urchins, they all have five-pointed body structures and usually boast some sort of spiny surface. There are around 7,000 species within the phylum, making it the largest marine phylum in the animal kingdom.
Sand Dollar Appearance
Sand Dollars are usually between three and four inches across. They are shaped as irregular circles, measured by their diameter. Their skeleton is called a test and is arranged in five points. This is the portion that most collectors see on the beach. While Sand Dollars are alive, their test is covered with soft spines and cilia, fine hairs. This helps the Sand Dollar move under the water.
When you find a Sand Dollar on the beach, chances are its spines and cilia will no longer be present. Instead, the test is bleached white. It still has a five-point structure design. This design is actually made of five symmetrical pairs of lines. They are the pores in the skeleton that allow the Sand Dollar to exchange gasses. When they are alive in the ocean, Sand Dollars are purplish-gray, with the color varying depending on the species. This color comes from the spines and cilia on the surface of their skeletons.
The Sand Dollar’s mouth is located on the bottom at the center. The Sand Dollar’s anus is located to the side, which is unique among sea urchins. Some Sand Dollar species also have slits in their skeleton, called lunules. These remain even after the Sand Dollar has died and their skeleton washes up on the beach. Lunules help them embed deeper in the sand without getting washed away in the current or ocean waves.
Distribution, Population, and Habitat
Sand Dollars are common in warm waters as well as temperate areas. Many species live off the coasts of Central America and South America. Some also live as far north as Florida and the eastern coast of the United States. Sand Dollars are also found on the Pacific coast, from Alaska all the way to Mexico.
They live in shallow water as well as deeper ocean habitats over 100 feet. As long as they have food to eat and sand to burrow in, Sand Dollars are happy. They bury themselves in the sand and often live in groups, both for reproduction and because they congregate where food is plentiful.
Sand Dollars are not endangered but people are still discouraged from collecting or trawling for them. In fact, in most areas, taking a live Sand Dollar specimen is illegal. Trawling on the sea floor can also be illegal. This environment is very fragile and supports a variety of ocean life. The Sand Dollars are just one of many types of sea animals that live on the ocean floor. While they may not be in danger of declining population numbers, changes in their habitat can have disastrous consequences for other more vulnerable species.
Predators and Prey
Sand Dollar spines are used for movement rather than defense or offense. Their hard exoskeleton provides some deterrent for potential predators. However, fish such as Cod and Flounder do eat Sand Dollars. Humans can also become predators for Sand Dollars, taking specimens from the ocean for collections. This is illegal in many areas, however.
Sand Dollars feast on algae and other small particles in the ocean water. They can use their spines to move along the sea floor to get to additional patches of algae. Some species turn on their side to get algae that are floating in the water. This is less common, however. They also sometimes eat crustacean larvae.
Reproduction and Lifespan
Sand Dollars can be male or female. They reproduce externally. This means that both male and female Sand Dollars release gametes into the water, where fertilization occurs. The young are called larvae, which then grow and develop into adult Sand Dollars.
Sand Dollar larvae can also clone themselves when they feel threatened. They divide into two distinct specimens and each continues to grow and develop. These clones end up being smaller than the original larvae. Scientists think that this may help them escape the notice of predators better due to their smaller size.
Sand Dollars in Fishing and Cooking
It is illegal in most areas to fish for or collect live Sand Dollars. This is due to the fragile nature of their environment more than the risk of extinction. Sand Dollars are favorites among collectors because of their flower-like design on the front and stark white skeleton. You can usually take Sand Dollar skeletons that you find on the beach home with you, although you should always double-check the local regulations.
Some legends say that Sand Dollars are actually the currency used by mermaids or in the mythical city of Atlantis. It has also been associated with the Star of Bethlehem or an Easter Lily in Christianity.
Bakers can replicate the pattern of Sand Dollars by making cookies that also feature a five-pointed design on the front. Sugar cookies with almonds arranged in the same pattern are a fun way to give a nod to Sand Dollars at your next get-together.
Similar Sea Urchins to Sand Dollars
Sea Stars: These also have a five-point structure, although they do not possess the same kind of exoskeleton. These relatives of the Sand Dollar also make popular ocean specimens in your collection, although make sure that you only collect dead sea stars.
Sea Cucumber: These animals also live on the sandy sea floor and have spiny, leathery skin. They are shaped like a cucumber that can move, which gives them their name.View all 248 animals that start with S
Sand Dollar FAQs (Frequently Asked Questions)
How long can Sand Dollars live out of the water?
Sand Dollars can only survive for a few minutes out of the water. If you see a Sand Dollar washed up on the beach and it is stark white without any spines, it is already dead and you are actually looking at its skeleton. If it still has spines attached, get it back into the water right away.
How can you tell how old a Sand Dollar is?
The exoskeleton of a Sand Dollar has rings that tell how long it has been alive. Scientists can count the rings and look at other growth and development features to determine the age of a Sand Dollar.
How long does it take for a Sand Dollar to turn white?
Sand Dollars turn white within just 24 hours of washing up on shore. Once their spines and cilia fall off, the process begins. When you see a white Sand Dollar on the beach, you are actually looking at the animal’s skeleton.
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- New York Times, Available here: https://www.nytimes.com/2011/01/09/us/09bcintel.html#:~:text=The%20sand%20dollar%20is%20actually,excentricus%2C%20is%20perhaps%20the%20strangest.&text=Dendraster%20excentricus%20ranges%20from%20Alaska,to%20300%20feet%20of%20water.
- Monterey Bay Aquarium, Available here: https://www.montereybayaquarium.org/animals/animals-a-to-z/sand-dollar
- Oregon Coast Aquarium, Available here: https://aquarium.org/animals/sand-dollars/