What’s Inside A Sand Dollar?
There are plenty of places where you can find sand dollars on the beach. When for the first time I found one myself, I wondered what this beautiful shell is. Not a lot of people know that these shells were actually living marine animals that belong to the phylum Echinodermata and are very close relatives of sea urchins or sea stars. The white shell that you may find on the beach, is actually a dead sand dollar. If you found one and wondering what you can find if you break it open, here is the quick answer:
Inside a sand dollar, you can find its five teeth with a characteristic “V” shape. You can also find the remains of sand dollar’s food, which is mostly sand and small grains of magnetite that young sand dollar collects in order to be havier and not be washed away by the current.
However, that certainly doesn’t tell the whole story. Below I’ll explain in more detail what you can find inside a sand dollar and what the legend says about it. Furthermore, I’ll explain how easy it is to break a sand dollar shell, and what’s inside this living animal.
What’s inside a dead sand dollar?
First of all, if you find a non-harmful sand dollar and wondering what you can find inside if you break it open, make sure this animal is dead. If you’re not sure if the sand dollar you found is dead or alive, you can scroll to the bottom of this post to read more about it or go to my other post explaining the difference between a dead and alive sand dollar.
If you pick up a sand dollar’s skeleton (called test) and shake it gently, you may hear something moving inside. Those are probably a sand dollar’s teeth. Sand dollars when alive move around the sandy seafloor with their mouth side down. They have tiny spines around their body that help them to move but also to transport one by one, food to the mouth opening.
Their mouth has a jaw with five tiny teeth sections that help them to grind up the sand, chewing encrusting organisms and microscopic algae. If you break down the sand dollar’s called test, you’ll probably find its teeth, each with a characteristic “V” shape. They are often referred to as white birds.
What you can also find, are the remains of the sand dollar’s food. Sand dollars mostly eat detritus (dead particulate organic material), planktons, crustacean larvae, and debris from the seafloor. They pick up sand grains one by one and like mentioned above, they use their spines to move them to the mouth. That means you may also find sand inside a sand dollar.
What’s fascinating, you may also notice magnetic mineral parts after breaking “the shell”. How? Well, sand dollars in order to stay on the bottom during strong currents and not be washed away, eat sand to weigh more. The young sand dollars however may need a little bit more than that.
They pick small grains of magnetite from the sand and store them in chambers of their gut called diverticula. They use diverticula as weight belts, and exactly like divers use theirs, they help them to stay on the bottom. This iron-rich mineral weighs young sand dollars down, keeping them grounded until they grow bigger and heavier so they’re not washed away by currents.
In the video below you can see a sand dollar breaking open:
The legend about the sand dollar and the doves
What’s worth knowing is that there’s a legend associated with sand dollar’s teeth that are looking like white doves. Souvenirs shops very often sell sand dollars with a poem attached to them. The part of the poem says that once the sand dollar is broken open, the five doves (which are sand dollar’s teeth) are released to spread goodwill and peace:
“Now break the center open
And here you will release,
The five white doves awaiting
To spread Good Will and Peace.”
The Christian author also mentions in the poem the holes in the sand dollar’s skeleton. They represent the wounds on Christ when on the cross. The flower shape pattern represents Christmas Poinsettia, and on the other side of the sand dollar – star shape – represents the star of Bethlehem. You can read the full poem here.
Do sand dollars break easily?
Sand dollars skeletons will most likely break easily. When the sand dollar is alive, it has short spines and its color ranges from dark green to purple color. When dead, its spines fell off and the sun bleaches the shell what eventually turns is into a white color. Because of the sun, the shell becomes extremely fragile and is easily breakable.
If the sand dollar you’ve found is rocky-hard and unbreakable, it’s probably a fossil. Fossils are remains (or traces) of ancient animals. They can preserve entire organisms or small parts by natural processes. There are some sand dollars fossils found approximately 150-50 million years ago.
If you’d like to keep the sand dollar but the shell is too easily breakable, you can see my other post here where you can read more about how to preserve a dead sand dollar and harden its shell.
What’s inside living sand dollars?
Living sand dollars look totally different. They are covered in tiny spines that help them move around the ocean floor, bury themselves in the sand, and feed themselves. If you look closely, you can see them moving. Their color, instead of white, ranges from dark brown to purplish-red so they can stay camouflaged on the seafloor. The color may differ depending on the species since there are more than 200 of them! So this is what’s the top “layer” is.
Inside that, there’s a skeleton that we talked about above with a full complete digestive system. Sand dollars have mouth in the center of the bottom side of their body and the anus located on the edge of their test.
Once the food is in the sand dollar’s mouth, it moves into the esophagus. This tube is made up of two parts – the upper and lower. The upper part contracts to transport the food to the lower esophagus. The contractions push the food into the stomach where digestive enzymes break down the nutrients so they can be absorbed into the sand dollar’s body. Next, the waste passes through the intestine and is discharged through the anus.
Sand dollars (which look like old silver dollars, which is how they got their name) are one of the most interesting marine creatures and like every organism, they play an important role in our ecosystem. They control the population of smaller invertebrates and serve as a food source for some larger predators. After their death, they provide a source of calcium carbonate to our oceans. Eventually, this source combined with seawater helps other animals and plants to build their shells. It’s important to know that every organism is an important part of our ecosystem, and it’s always better to leave them where they were found.
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I’m glad to see you here. This blog is created for all marine creature lovers by a bubbly diver - me, Dori :)