⏳💵 Sand dollars: Filthy rich in evolutionary wonder

Nothing quite says “beach house” like a sun-bleached sand dollar hanging on a bathroom wall. But to see the marine memento as mere decor is to miss the fascinating life story of the unusual sea creature. Yes, before sand dollars wash ashore and dry out in the sun they are very much alive. Shaped like flat, purple sea urchins, these creatures crawl across the ocean on hundreds of tiny stilts, scraping algae and microbes off sand particles with alien-like mouths. Scientists love them because they’re a laboratory for the study of evolution. Over the last 50 million years or so, sand dollars have developed all kinds of clever adaptations to their harsh environment—like consuming and storing metal particles to control buoyancy, much in the way that a scuba diver dons a weight belt to stay down. But scientists are hardly the only ones who find meaning in this unassuming creature’s story. 🐦 [Tweet this!]( 🌐 [View this email on the web]( Join the next chapter of Quartz by downloading [our new app]( or becoming a [member](. It’s where the future gets its news. Sponsored by [Quartz Obsession] Sand dollars November 26, 2018 Coins come alive --------------------------------------------------------------- Nothing quite says “beach house” like a sun-bleached sand dollar hanging on a bathroom wall. But to see the marine memento as mere decor is to miss the fascinating life story of the unusual sea creature. Yes, before sand dollars wash ashore and dry out in the sun they are very much alive. Shaped like flat, purple sea urchins, these creatures crawl across the ocean on hundreds of tiny stilts, scraping algae and microbes off sand particles with alien-like mouths. Scientists love them because they’re a laboratory for the study of evolution. Over the last 50 million years or so, sand dollars have developed all kinds of clever adaptations to their harsh environment—like consuming and storing metal particles to control buoyancy, much in the way that a scuba diver dons a weight belt to stay down. But scientists are hardly the only ones who find meaning in this unassuming creature’s story. 🐦 [Tweet this!]( 🌐 [View this email on the web]( Join the next chapter of Quartz by downloading [our new app]( or becoming a [member](. It’s where the future gets its news. By the digits [250:]( Species of sand dollars still in existence worldwide, relative to some 750 fossilized species that have been described [$40,000:]( Value in stolen sand dollars that were snatched from a Florida woman’s home last year [$7:]( Cost of 50 sand dollars sold in a basket by Oriental Trading Company [$500:]( Fine for taking live sand dollars from the beach in Hilton Head, South Carolina [15:]( Diameter, in centimeters, of the Guinness World Record-holding sand dollar [6-10:]( Typical lifespan, in years, of a sand dollar Field guide What exactly are sand dollars? --------------------------------------------------------------- Hedgehogs of the sea. Well not quite, but they’re members of the phylum Echinodermata, a term which translates roughly to “hedgehog skin.” It includes things like sea urchins, stars, and cucumbers—and the more recently discovered “[headless chicken monster]( of which have a prickly and protective outer layer. Sand dollars are actually a kind of irregular sea urchin. Like their close relatives, they’re covered in hundreds of spines, [which they use like legs]( to traverse the ocean floor. And they, too, have an appetite for algae and bacteria. What makes them stand out is that … they don’t. Sand dollars have taken up residence on the sandy sea bottom, where there’s nothing to hold onto when the current picks up. And so they’ve evolved an array of impressive tactics to avoid being swept away, such as a flat body and the ability to burrow. “If you imagine yourself riding into the wind on a bicycle, you find yourself hunching over to get down out of the wind,” Rich Mooi, a researcher at the California Academy of Science, [told KQED](. “You’re trying to minimize drag. That’s what sand dollars have done.” Many sand dollars are coin-thin, but there are some exceptions—like the so-called sea biscuit or [cake urchin]( (not to be confused with “sea cookie,” the general term that New Zealanders use for sand dollars). Although they, too, are considered sand dollars, they tend to be a little plumper. Sponsored by Blockchains, LLC You always wanted to change the world. --------------------------------------------------------------- Did you do it or did the world end up changing you? It's time to break away from the status quo and make new systems, new security, and new interactions. We can create a world that makes everything we do work better, using the blockchain.[Are you ready to change the world?]( Fun fact! When sand dollar larvae detect a predator they split in two. In [a 2008 study]( researchers exposed the tiny free-floaters to fish mucous, a signal that predators were near. In response, the larvae developed “clone buds” that popped off and turned into new, smaller, and genetically-identical larvae. Smaller larvae, the authors reasoned, are less likely to be detected by predators. Giphy Pop quiz What’s in the name? Early discoverers thought they looked like dollar coins.They cost around a dollar each when they were discovered centuries ago.Once abundant on beaches, you could earn dollars removing them.As legend has it, they were used as currency in the lost city of Atlantis. Correct. Occam’s razor strikes again. Incorrect. If your inbox doesn’t support this quiz, find the solution at bottom of email. One-of-a-kind Odd specimens --------------------------------------------------------------- The eccentric sand dollar is the common name of a US West Coast species that goes against sand dollar norms. For one, it grows lopsided: The urchin’s feeding mechanism, anus, and other organs are [offset to one side of the body]( as if designed by a drunk. But evolution isn’t sloppy. Dendraster excentricus, as it’s known in science, lives its life in an unusual position—“with its front end stuck into the sand like a coin upright in clay,” Rich Mooi told Quartz by email. That way, it can nab bits of algae drifting by in a current “instead of eating the food particles in the sand itself as all other sand dollar species do.” If its body parts weren’t offset, many of them would be buried in the sand and thus not accessible to make this clever trick advantageous. Relative to other species, Excentricus is also more communal. While most sand dollars live out their days alone (they mate without contact, by releasing sperm and eggs into the water around the same time), Excentricus inhabits dense, sand-dollar cities, with as many as [625 individuals]( per square yard. Giphy The kid’s menu A meal of metal --------------------------------------------------------------- Being lean goes only so far in preventing sand dollars from getting caught up in a current. They also have to be heavy. While older dollars naturally weigh more, freshly minted urchins need supplements to bulk up. Really. As they sift through the sand, [they search for minerals comprised of metals like magnetite]( which they ingest and store in their gut. The more metal they take in, the heavier they become. And the less likely they are to drift away. Quotable “Not very good.” —[Dr. Rich Mooi, a curator at the Academy of Sciences, on the taste of sand dollars.]( (The gonads of other urchins are considered a delicacy.) Watch this! As sand dollars evolved to reduce drag, they basically turned into airplane wings. That created another problem: lift. It’s good for airplanes but bad for ocean-floor-feeding urchins. So they evolved a workaround—holes to equalize pressure and cut lift. Because religion! Birth, crucifixion, and resurrection --------------------------------------------------------------- If you find yourself browsing sand dollars in a seaside souvenir shop, chances are you’ll come across a poem—the Legend of the Sand Dollar. [“The legend of the sand dollarThat I would like to tellOf the birth and death of Jesus ChristFound in this lowly shell.”]( It may seem odd to ascribe so much Catholic meaning to a sea urchin, but the believers see: - The five-petal design adorning the sand dollar, created by the creature’s tube feet, which looks a little bit like the Star of Bethlehem - Holes in the urchin’s skeleton, which help reduce drag, as representing Jesus’ wounds during the crucifixion - The outline of a Christmas poinsettia on the flat bottom of the sand dollar And perhaps most significantly, if you snap open a sand dollar skeleton, five little pieces fall out. Depending on who you ask, those are parts of the creature’s jaw … or five [“doves of peace.”]( Glossary ☠Test: The skeleton of a sea urchin, made of five calcium carbonate plates arranged in a radial pattern. 🏮Aristotle’s lantern: As you would absolutely never guess, this refers to the mouth of a sand dollar. Aristotle first described the apparatus, which he thought looked like a lantern, in the 4th century BC in the book Historia Animalium. 🌸Petaloid: The star-like pattern on the surface of a sand dollar. When they’re alive, the petaloid houses specialized “tube feet” that absorb oxygen from the water. 🕳Lunules: Slits or holes in the skeleton of a sand dollar that reduce lift as water passes by. 🏋️‍Diverticula: Chambers in the gut where sand dollars store metal-rich mineral deposits. Like weight belts, the metals help the urchins stay down. Giphy Poll Be honest: Did you know sand dollars were living sea creatures? [Click here to vote]( YesNo, this is shockingI’m still not convinced 💬let's talk! In Wednesday’s poll about [dog shows]( 40% of you say you watch Best in Show as often as you can, while 33% said you’d never heard of it. ⭐ [Become a Quartz member]( 🗯 [Discuss on the new Quartz app!]( ✏️ [What did you think of today’s email?](mailto:obsession%2Bfeedback@qz.com?cc=&subject=Thoughts%20about%20sand%20dollars&body=) 💡 [What should we obsess over next?](mailto:obsession%2Bideas@qz.com?cc=&subject=Obsess%20over%20this%20next.&body=) 📬 [Forward this email to a friend](mailto:replace_with_friends_email@qz.com?cc=obsession%2Bforward@qz.com&subject=%F0%9F%92%B5%20Sand%20dollars%3A%20Filthy%20rich%20in%20evolutionary%20wonder&body=Thought%20you%27d%20enjoy.%20%0ARead%20it%20here%20%E2%80%93%20http%3A%2F%2Fqz.com%2Femail%2Fquartz-obsession%2F1474424) 🎁 [Get the Quartz Tabsession Chrome Extension]( 🌊 [Dive into the archive]( Today’s email was written by [Benji Jones]( edited by [Jessanne Collins]( and produced by [Luiz Romero](. The correct answer to the quiz is Early discoverers thought they looked like dollar coins.. Enjoying the Quartz Obsession? [Send this link]( to a friend! If you click a link to an e-commerce site and make a purchase, we may receive a small cut of the revenue, which helps support our ambitious journalism. See [here]( for more information. Not enjoying it? No worries. [Click here]( to unsubscribe. Quartz | 675 Avenue of the Americas, 4th Fl | New York, NY 10011 | United States [Share this email](