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Live Sand Dollars in Costa Rica
Live Sand Dollars
Sand Dollars and Math
One day at the beach in Costa Rica my daughter and I were digging in the sand making sandcastles when we ran across a live sand dollar. Finding a dead exoskeleton would have been exciting but finding a live sand dollar was unbelievable!
We held it in our hands and felt the tiny hairs on the underside of its body tickle our skin as the animal tried to get away from us and wiggle its way back down into the sand. We turned it over and watched its mouth moving in the center of its flat body.We set it down in the sand and watched it filter sand and water through its body and out the five holes that radiate out from the center.
Then we started to feel just under the surface of the sand as the tide washes the waves back and forth and began to find more sand dollars. At first we found one or two. Then we found them by the tens. We soon realized that there were hundreds, thousands and possibly millions of sand dollars right there on that beach.
Talk about a teaching moment!
We spent the rest of the day observing, drawing, measuring and counting sand dollars. This lens is about the math that can be learned at the beach while observing sand dollars.
Finding Math at the Beach - Disappearing Sand Dollar
Sand Dollars and Math
Many people think that math can only be found in textbooks, that learning only takes place in a classroom and that math is a boring but necessary evil.
The day we found the sand dollars was filled with fun and exciting activities that helped us describe our observations of the sand dollars while working on basic math skills. We spent the day observing, drawing, measuring and counting sand dollars.
Since then I have added many more activities to this unit study and found that children love to learn math when it involves the chance to learn in an exciting environment such as the beach and about a live animal living in that environment that they may never have seen before, such as the sand dollar.
Math that can be learned at the beach while observing sand dollarsl
Math Day with the Sand Dollars
What do you need for your day at the Beach?
- Plenty of sunscreen
- Water to drink.
- An underwater clipboard
- A waterproof digital camera
- A guidebook to the seashore (keep in a Ziploc bag)
You also might like a stopwatch to see how fast the sand dollars can bury themselves back under the sand, a compass to see if they always go into the sand in the same direction and a tape measure to measure the diameter of the sand dollars.
I keep these things in a bag in the back of my car so that we are always prepared for unexpected math adventures at the beach.
Counting Sand Dollars
Adding, Multiplying and even Dividing Sand Dollars
As you walk along the beach you will find many beautiful shells, pieces of seaweed and sand dollar tests, "sand dollar shells". It can be fun to collect them and then use them in counting games.
For very young children that might mean just count to 3 or 5. For older children you might arrange them into groups of 10 and then count by tens to see how many you have collected.
You probably won't find hundreds of sand dollars but if you find say, five sand dollar tests, each with five holes you can multiply to see how many holes there are all together.
What if you wanted to pretend to feed a pile of 20 small shells to the sand dollars. How could you divide those shells evenly among the sand dollars?
How Old is your Sand Dollar? - Calculating the Age of a Sand Dollar
Sand Dollar Ridges
Look for the hard white sand dollars along the tideline amongst the seaweed and shells. These are the exoskeletons or the dead remains of sand dollars. Look for growth rings along the edges of these plates.
Separate your sand dollar tests (the dead "shell" of the sand dollar) by age. What is the average at which your sand dollars died?
You can use your underwater tablet to make a graph representing the average lifespan of the sand dollars you found on the beach.
- Sand Dollar Printout
You can often find the dead "shell" of a sand dollar (called a "test") washed up on sandy beaches. If you break open a test, there are many hard, loose, white pieces; these were the teeth of the Sand Dollar. - Enchanted Learning Software
- Intertidal invertebrates of California
Scientists can age a sand dollar by counting the growth rings on the plates of the exoskeleton. Sand dollars usually live six to 10 years. - Google Book Search
Sand Dollar Symmetry - Symmetry at the Beach
Looking for Symmetry in Sand dollars
Study the exoskeleton of a sand dollar and you will quickly find the line of symmetry that divides it into two equal parts.
- Sand Dollar Symmetry
Like other echinoderms, sand dollars have fivefold radial symmetry (pentamerism). Unlike sea urchins, the sand dollar has secondary bilateral symmetry, with a front and back as well as a top and bottom. The anus is toward the rear rather than on the
Sand Dollar Worksheets
For the younger children it's fun to print out these sand dollars and try to find the two that match.
For the older children, challenge them to make more Sand Dollar Twins.
- Sand Dollar Activity Page - Find The Twins
- What Are Echinoderms?
In this science printable about invertebrates, students will evaluate true/false statements about echinoderms and use reference materials to identify drawings of a sea cucumber, a starfish, a sand dollar, and a sea urchin.
- Marine Biology Game
I Am a Marine Invertebrate. Here are the names of the animals found in this quiz.
Sand Dollar Number Line - Counting by 5's with Sand Dollars
When you get back home you can start a number line using sand dollar mini accents for the multiples of 5. We used blank squares for the numbers 1-4, a sand dollar paper for 5 and then again blank squares for 6-9.
We also used the sand dollar mini accents for writing the numbers 1-5 next to each of the holes in the sand dollar and then writing a large 5 in the middle. One of my children really enjoyed this activity and continued on up to 100.
Later on we used these to remember the numbers that come right before the multiples of 5 when subtracting. We played a game like a spelling bee and used the cards when asking questions like what number is 3 less than 10.
Watching the movements of a Sand Dollar - Measuring the Speed of a Sand Dollar
Notice how the hairs on the edge of the sand dollar move in waves to help the sand dollar to travel across the sand. The sand dollar leaves circles showing that there are more rows of hairs on the underside of its body helping it move.
Using a tape measure and a stop watch you can determine the speed of a sand dollar. How many inches per minute can a sand dollar travel? How long would it take the sand dollar to travel a yard or a meter? a mile?
Does the sand dollar always head toward its shadow? What happens if you block the sun? Can blocking the sun confuse the sand dollar's sense of direction? If you measure the length of the sand dollar's shadow and its height can you determine the angle of the sun?
A beach in Costa Rica is the perfect classroom for homeschooling.
Sand Dollars found at the Beach
Finding Sand Dollars on the Beach
Sand dollars can be found on the beach just under the sand at low tide in the tidal zone. Run your hands through the water saturated sand to feel for them. The are not harmful and do not bite. When you hold them in your hands they tickle as their hairs quickly move trying to get back down under the sand.
Sand dollars need to stay moist so don't keep them out of the water very long.
Sand Dollars at the Edge of the Tide
Comparing Live Sand Dollars with their Tests
Look for the tests of sand dollars that wash up with the seaweed at the tide line. These are the white remains of dead sand dollars that some call the shells. Compare the tests with the live sand dollars. Try to find ones of similar size and compare them. How much space does the live sand dollar take up in comparison to its test?
Holding a Live Sand Dollar
Picking up a Live Sand Dollar
Sand Dollars are fine to pick up. They don't bite, sting or give you a rash. The bottom side of the sand dollar is covered with suction cups that tickle as the sand dollar glides across your hand. Turn it over to see the suction cups. Remember to return the sand dollar to where you found it after just a short time as the sand dollar needs to be in the water to breath.
Doves in the Sand Dollar
- Spider Magazine - www.SpiderMagKids.com - How to Clean a Sand Dollar
Have you been lucky enough to find a sand dollar this summer? Find out how to clean and preserve it so you can enjoy putting it on display.
- How to preserve and harden a Sand dollar
One of the keys to cleaning a live sand dollar is also very often the least known. In order to get a sand dollar to bleach white it is important to soak it in fresh water first. Here are the steps you should follow in order to ...
Sand Dollar Cookies
Making Sand Dollar Cookies
Now that you are back from the beach it's time to whip up a batch of Sand Dollar Cookies. Use fractions to measure the ingredients. The more the merrier so use your knowledge to multiple fractions as you double or triple the recipe.
Once the cookies come out of the oven it's time to divide them equally.
If there is no time to make the cookies you can't do better than to order some from Plum Island Cookie Company. Figure out the cost including tax, handling and shipping. How much would that be if you order two boxes?
How many cookies will there be for each person in your family if you divide them equally? How about if you invite your grandparents?
Sand Dollar Cookie Ingredients:
* 3/4 C butter
* 1 cup sugar
* 2 eggs
* 1/2 Teas. vanilla
* 2 1/2 C flour
* 1 Teas. baking powder
* 1 Teas. salt
1. Mix the butter, sugar, eggs, and vanilla thoroughly.
2. Add flour, baking powder and salt.
3. Mix and chill the dough for one hour.
4. Roll out the dough on a floured surface to 1/8"-1/4" thick.
5. Cut out cookies using a 3" cutter or water glass.
6. Place cookies on ungreased cookie sheet.
7. Draw a star in the center of each cookie with a dull knife.
8. Bake at 400 degrees for 7 mins.
Recipe Credit: Cape Treasures
- Etsy :: Dmari :: Plum Island Cookie Company Sand Dollar Cookies
Plum Island Cookie Company is a small specialty bakery offering delicious Gourmet French Butter cookies hand-designed into exquisite Sand Dollars and other buttery sweets! The delicate vanilla-scented butter cookies come boxed with fou...
Dividing the Sand Dollar Cookies - Sand Dollar Division
Read the story of the children trying to divide the cookies evenly as more and more friends show up at the door in the story The Doorbell Rang. Then make some sand dollar cookies and practice some division and of course, subtraction.
Playdough Sand Dollars - Make your own Sand Dollars
Mix up some Playdough and add some sand. Make your own playdough sand dollars. Use the test of real sand dollars to press the details of the sand dollars into the ones you are making.
Once you have a pile of Sand Dollars you can use them as math manipulatives, adding and subtracting them from a beach in the sensory table.
How else could you use your playdough Sand Dollars?
Home Made Playdough
1 cup flour
1 cup of water
1/2 cup of salt
2 tablespoons Cream of Tarter
1 tablespoon of Oil
Cook this ingredients until it forms an item in the pan. Pour it out onto a Tupperware lid. Cover with damp cloth. Add food coloring if you like. Store new playdough in the fridge in an airtight container. This is non-eatable playdough.
Sand Play Dough
1/2 cup sand
1/2 cup cornstarch
1/2 cup boiling water
Mix ingredients together and knead.
Sand Dollar development - From Fertilization of the Sand Dollar Egg to Zygote
Fertilization through the fourth or fifth cleavage event of a sand dollar. Watch the membrane of the Sand Dollar's egg begin to develop and then see the cells divide. How many cells are there by the end of the video?
We found live sand dollars on a beach in Costa Rica!
A day at the beach can be filled with amazing learning experiences. Take time to observe, spend time exploring, look for the unusual in ordinary experiences. Each day, each place you visit can be filled with wonder.
Come write about your experiences learning and teaching while vacationing in such beautiful places as Costa Rica on Wizzley, a fun and easy place to express your opinion:
Costa Rica's Sand Dollars
I'd like to suggest that we all take a trip to a beach to Costa Rica and learn a bit of math...