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# Live Sand Dollars in Costa Rica

## 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.

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.

## 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

## 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.

## 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?

## 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

## 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 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.

## 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.

## 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?

## 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

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?

* 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

Procedure:

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.

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

## 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?

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

## 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?

## Sand Dollars

### 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...

## Sand Dollar Beach Day Discussion - What math have you learned at the beach?

fcinternetmarketing on July 22, 2013:

Very interesting Sand Dollar"s lesson.Great lens.

Cynthia Haltom from Diamondhead on May 13, 2013:

I spent a summer in Costa Rica learning Spanish, but I never came across live sand dollars. How exciting to see them live. Maybe next time I go I will look for them.

ohcaroline on February 15, 2013:

I enjoyed this sand dollar lesson. Very interesting.

Michey LM on February 15, 2013:

Beautiful lens and very informative for me. We have a couple of those but I have no idea that we call them sand-dollar.

dahlia369 on February 13, 2013:

It seems to me you're the most ingenious person I know of - to turn any experience into a fun teaching lesson for kids. Congrats!! :)

Nathalie Roy from France (Canadian expat) on January 10, 2013:

sand dollars are one of the most interesting sea creatures

Rhonda Albom from New Zealand on January 09, 2013:

Wonderful information on sand dollars. We find them all the time where we live, but I never knew we could learn their age. You know what I am doing tomorrow. - Squid Angel Blessed.

akunsquidoku on August 03, 2012:

very interesting..:D

Joan Haines on July 07, 2012:

Your suggestions are wonderful. Let's all go to Costa Rica now! "Squid Angel blessed."

bbsoulful2 on July 03, 2012:

Your lenses are always so beautiful, Evelyn - thank you!

So much sandy fun in learning about sand dollars :)

fivee05 lm on June 21, 2012:

An interesting lens!

RuralFloridaLiving on June 21, 2012:

Wow - very interesting lens. I've always loved sand dollars but never knew a thing about them. Thanks a lot!

Close2Art LM on June 21, 2012:

I wonder why they are called sand dollars? great lens, Blessed

savateuse on June 21, 2012:

Excellent lens!

Mary Crowther from Havre de Grace on June 20, 2012:

I like the play dough sand dollars, wonderful idea!

Sand Dollars are so beautiful and unique! Great lens.

Renaissance Woman from Colorado on June 20, 2012:

What a great set of lessons. Wow. I learned so much about sand dollars. They are such favorites of mine. I've never found a live sand dollar, but do have an extensive collection of exoskeletons from when I lived on Padre Island. I can see how exciting it would be for children to experience sand dollars and all of the living lessons that they provide. Thanks for another outstanding learning presentation. Appreciated!

cleanyoucar on June 19, 2012:

Great information, you learn something new everyday

xXOUTDOORSXx on June 19, 2012:

cool lens

lucky izan on June 18, 2012:

it's really look like a coin, no wonder it called sand dollar

fullofshoes on June 18, 2012:

Once again, I am fascinated by the content of your lenses. I love to learn new things and your work is full of fun and interesting "stuff". very ~blessed~ !

davecurrtis on June 18, 2012:

This is a great way to learn math, nice idea.

Stephanie Tietjen from Albuquerque, New Mexico on June 18, 2012:

The grains of sand like to be counted. If the sand is not too fine, you can do it. I think this is a fantastic lesson, I love sand dollars, and might have loved math more with a lesson like this. Your kids are so lucky that you are their teacher.

Ellen Gregory from Connecticut, USA on June 18, 2012:

What an interesting lens. Beautifully done.

slotowngal on June 18, 2012:

Oh, I love sand dollars! We used to collect them on the beach in California when I was a girl, but I had no clue about most of the wonderful sand dollar info in your lens. Thank you so much for a beautiful look at sand dollars (and math)! angel blessed.

rallo-smith on June 18, 2012:

Lots of great information here. I love it when I learn new things. Thanks for sharing.

writerkath on June 18, 2012:

Hi Evelyn! This is a fabulous lens! Perfect teaching medium in so many ways, and for so many disciplines. Beautiful! Sometimes, when my husband &amp; I walk on the beach, we'll see a partial sand dollar and remark "Oh, look! A sand-50-cent piece" or "Just saw a Sand-Quarter!" :) I learned a lot from this lens, and thank you for taking the time to put it together. *Blessed!* :)

Anthony Altorenna from Connecticut on June 18, 2012:

It's always fun to search the tide pools at low tide. There's an area near our beach house where we can find sand dollars, starfish and crabs.

intermarks on June 18, 2012:

I have recently found a sand dollar in the beach and now only I know it is called sand dollar. This is really a beautiful natural creature.

anonymous on June 17, 2012:

Very informative. Thanks for sharing.

kindoak on June 17, 2012:

Super excellent! I remember these from my childhood abroad.

Mary Norton from Ontario, Canada on June 17, 2012:

I have not seen a live sand dollar. I would love to have your experience.

SteveKaye on June 17, 2012:

You create the most interesting lenses. Thank you for publishing this one. I found the info on Sand Dollars to be fascinating.

MrInfopreneur on June 17, 2012:

I had no idea what a sand dollar was till I stumbled upon your lens :)

Lisa Morris on June 15, 2012:

Congratulations on the purple star! This lens has a lot of great information on the sand dollar. I love sand dollars. Blessings.

Robin S from USA on June 15, 2012:

Like #100. Congratulations!

amberchina on May 23, 2012:

Sand dollars are just so stinkin' cool! Your lens has so many great ideas for parents and children to do together this summer to retain learning, so I just featured your lens on my "The Best Summer Learning Activities and Projects by Subject" lens. I know it will be helpful to even more parents and kiddos. :)

Joanie Ruppel from Keller, Texas on January 31, 2012:

I found some live sand dollars in the Aegean Sea off the coast of Turkey. Had to go to 8 feet deep to scoop them up in very salty water, not east to do, but worth the prize. I took one out, snapped a picture, and returned it to the sea where it belonged. Very interesting lens.

TransplantedSoul on December 31, 2011:

These are such beautiful animals. This lense makes me want to be on the beach right now!

liberia88 on September 29, 2011:

It was fun exploring this page. There is a lot of great information. I would love to see live sand dollars too!! I will have to look for them when I go snorkeling on the Pacific coasts of Guanacaste, Costa Rica.

mommy2deb on September 25, 2011:

Interesting lens.

Moe Wood from Eastern Ontario on June 13, 2011:

We never learned math at the beach but I think it is a good activity to incorporate.

Snakesmom on May 19, 2011:

Beautiful lens! I love the sand dollars, they are so cool!

akumar46 lm on May 19, 2011:

What a cool Sand Dollar math lessons!Thanks.

CherylsArt on May 19, 2011:

What an amazing find, and such a wonderful teaching moment.

Sharlee on April 15, 2011:

wonderful lens! Shar

Julia M S Pearce from Melbourne, Australia on January 05, 2011:

Aren't they lovely.I love shells.We used to find counters on the beach as kids.

Violin-Student on January 05, 2011:

Great page (as usual). Thanks!

Art Haule

ChrisDay LM on December 31, 2010:

Great lens - home education is THE thing!

BrickHouseFabrics on December 21, 2010:

Wonderful lens about something that has always intrigued me!

sorana lm on December 11, 2010:

Evelyn your lenses are so creative and inspiring. Yet another wonderful one. Thanks

irenemaria from Sweden on December 10, 2010:

Sand dollar is exotic to me. But what I really loved about this is, how you and your children were standing there feeling, watching and learning about this little guy. This is exactly the way my children were raised too.

anonymous on December 10, 2010:

Wonderful lense of Sand Dollars! Love to be here. Thanks for creating this natural lense :)

CruiseReady from East Central Florida on October 05, 2010:

What a fabulous lens!

caketech on September 16, 2010:

I truly loved this lens! Wonderful imagery and descriptions. I didn't know how to tell the age of a sand dollar until now. Great lens! Thanks for sharing your memory.

Evelyn Saenz (author) from Royalton on April 25, 2010:

@myraggededge: Thank you so much and Congratulations on becoming a SquidAngel :)

myraggededge on April 25, 2010:

Popped back here to bless this fabulous lens :-)

Heather Burns from Wexford, Ireland on April 10, 2010:

amazing sand dollar lens!

managdem on April 10, 2010:

Nice idea to teach math at beach with sand dollars. Actually, any beach an attractive environment to enjoy anything. So, Learning with sand dollars became enjoyable.

Thanks for sharing.

Louis Wery from Sarasota, Florida USA on April 10, 2010:

Thank you for showing us creative ways to learn. Beautiful lens!

kidspartythemes on February 20, 2010:

Excellent lens! I totally agree that the more creative ways in which we can teach our kids, the more engaged they will be! 5 stars x

Evelyn Saenz (author) from Royalton on December 11, 2009:

@ElizabethJeanAl: Teaching on the beach in Costa Rica is an ideal classroom.

ElizabethJeanAl on December 11, 2009:

What an interesting and unique way to teach.

Evelyn Saenz (author) from Royalton on September 08, 2009:

[in reply to AndyPo] Thank you, Andy

Andy-Po on September 07, 2009:

Excellent lens. Great idea.

sarita from Hisar on September 04, 2009:

Fantastic lens... Thanks for sharing.

Jennie Hennesay from Lubbock TX on September 03, 2009:

What a great, indepth article on sand dollars. You are a fantastic teacher-and I'm not a child. Well maybe I'm in my second childhood.

Frankie Kangas from California on August 29, 2009:

Wonderful lens. I've always loved sand dollars but didn't know anything about them live. I have a collection of some. The smallest is only about 1 in across. It's pretty cool. Bear hugs, Frankie

Terry Boroff (flipflopnana) from FL on August 20, 2009:

All I can say is what an awesome page! I loved everything about it.

Tom Fattes from Naperville, IL on August 19, 2009:

Great lens on Sand Dollars. I've always been a fan but never knew you can learn so much from them.

anonymous on July 02, 2009:

Very thorough and beautiful lens. I especially loved the sand dollar cookies!

Barkely on May 23, 2009:

Thanks for adding this lens to the Fun For Kids Group:-)

ElizabethJeanAl on May 19, 2009:

Hi,

My name is Elizabeth Jean Allen and I am the new group leader for the Nature and the Outdoors Group.

Lizzy

dustytoes on May 19, 2009:

I like the idea of teaching on a beach! What fun for any child. Lensrolling to my seashell lens!

kellywissink lm on May 16, 2009:

5 stars!

Welcome to the group Home Schooling Support Group-Kelly

anonymous on May 11, 2009:

I LOVE sand dollars! Have a wonderful birthday!!!!

Evelyn Saenz (author) from Royalton on May 10, 2009:

[in reply to KimGiancaterino] Thank you, SquidAngel.

KimGiancaterino on May 10, 2009:

One of my friends made me a shadow box with a broken sand dollar and "The Legend of the Sand Dollar" poem. The delicate pieces inside the sand dollar represent peace doves. It's really beautiful. I would like to see a live sand dollar someday. Squid Angel Blessed.

tandemonimom lm on April 25, 2009:

Beautiful and thorough, as usual! I love the sand dollar cookie cutters. Welcome to The Homeschooling Groups!

Susan Deppner from Arkansas USA on April 25, 2009:

I love teachable moments, love the beach, love this lens! Another winner by Evelyn, first class all the way as always!

Mortira on April 23, 2009:

What a great summer activity! According to Malcolm Gladwell, summer learning is essential to a child's intellectual development. And the more fun, the better, I say!

Welcome to the Four Seasons group!

This is an UBER GROOVY lens. It WILL be revisited when we study invertebrates!!!!

Evelyn -- we've been to Costa Rica, but didn't find any sand dollars! Again, another truly remarkable and engaging lens you've masterfully created.

Kiwisoutback from Massachusetts on April 17, 2009:

Well done! Great photos, too. I never realized sand dollars were so mathematical, but it makes sense now that you've explained it. Squid Angel blessed!

eclecticeducati1 on April 14, 2009:

Love this lens!! It makes me wish we lived near a beach. 5*

Nancy Tate Hellams from Pendleton, SC on April 12, 2009:

This is great. I love Sand Dollars but never thought about them as teaching tools. Wonderful idea and wonderful lens.

Patricia on April 10, 2009:

I love sanddollars. I used to collect them as a child.

dahlia369 on April 10, 2009:

Sand dollars are magical and beautiful and so is this lens - thank you for making it and sharing it... :)

Jimmie Quick from Memphis, TN, USA on April 09, 2009:

Who doesn't love sand dollars. I'm sure you know of the legend of the sand dollar too. Not math related, but wonderful symbollism of the Christian faith. Of course, please add this to the Learning and Teaching Math group. I'm also going to lensroll this to my Nature Study at the Beach lens.

motorpurrr on April 09, 2009:

Nice of you to write about snad dollars. I had no idea they even moved, nor so many subspecies. So cool, thanx.

Yvonne L B from Covington, LA on April 09, 2009:

Welcome to the Naturally Native Squids group. Don't forget to add your lens link to the appropriate plexo and vote for it.