The BioGeek Memoirs: Sand Dollar

I grew up in Southern California in the US not too far from beach towns. My parents would rent a cabin each summer and we spent weeks playing on the beach and in the surf. I spent many a morning playing with small animals along the beach like crabs and sea anemones and had a pretty good shell collection by the end of each summer. One of my very favorite early morning gleanings was the rare, perfect sand dollar.

Three perfect little sand dollars.

What I didn’t know as a child is that the sand dollars that I collected during early morning walks on the beach were just the skeletons of what was once a living animal that looked like this:

A living sand dollar. Credit: Frédéric Ducarme, CC BY-SA 4.0, via Wikimedia Commons

I collected many, many seashells each summer; these shells were created by the animals that lived in them when they secreted and deposited calcium carbonate outside their bodies. In the case of sand dollars, the animal deposits little calcium carbonate plates internally to create the inside skeleton made of the same material as shells are. Cool, right? I never suspected that the living sand dollar was covered with all of those short fuzzy spines that helped it bury itself in the sand where it can move around. Those little guys used to live off the shore of Southern California where I lived, moving though the sand, eating little bits of algae and whatever else they could find in the sand of the ocean bottom. Preyed upon by fish, the skeletons of the dead animals washed up on the shore where I found them.

In my high school years my family moved to a beach town. Woohoo! Beachcombing for sand dollars continued year-round! I dated (and later married) a guy who loved to surf; I poked around in tide pools while he was out catching waves. My love affair with all the living things in the shoreline ecosystem continued during those years; my collection of shells and sand dollars grew.

Imperial Beach, California. Best town ever for the BioGeek high schooler.

I continued to love sand dollars when I grew up. I learned in college that they, like all echinoderms, have bodies that are organized in a 5-part radial symmetry. Strange, right?! But true. All sea urchins, sand dollars (AKA sea biscuits), sea stars, and sea cucumbers have a clear 5-part body organized around a central point (that gives them their radial designation).

See the 5 arms of this sea star? When the animal was alive it looked the same no matter which arm was “down”: radial symmetry.

I have continued to accumulate sand dollars as an adult. One day I discovered 3 wonderful sand dollars in my mailbox at work: an anonymous gift from a student, I think. There was a silver and gold sand dollar necklace at a store I passed one day on a trip to San Fransisco: of course I bought it!! Then there was my trip to the Smithsonian in Washington, D.C. I saw a sand dollar fossil for sale in the gift shop.

Look at that! A fossil that is millions of years old that looks just like the sand dollars that I used to pick up on the beach as a child.

I am often struck with amazement at how this simple, simple creature has so successfully survived in its little niche over the millennia. Mostly defenseless, relying on guile, concealment, and luck, the species continues to this day.

Today my fossil sand dollar and one that I was gifted (upper right in the picture) hang out on a tray on my coffee table. I may no longer live in the beach town of my childhood, but the beach, and the animals that I loved as a child, remain with me.

Author: Midnight Knitter

I weave, knit and read in Aurora, Colorado where my garden lives. I have 2 sons, a knitting daughter-in-law, a grandson and two exceptionally spoiled kittens. In 2014 I was diagnosed with a serious rare autoimmune disease called systemic sclerosis along with Sjogren's Disease and fibromyalgia.

14 thoughts on “The BioGeek Memoirs: Sand Dollar”

  1. I used to love collecting sand dollars as a kid, too—though I don’t remember ever finding whole ones actually on the beach. I know I bought some from souvenir shops, though. And I remember feeling very awkward when I learned that they were skeletons.

    1. You had to get up really, really early to get a whole sand dollar on the beach! It is kind of creepy to have the remains of these animals on my coffee table, but I love them, so there they are.

  2. I haven’t ever seen a sand dollar washed up on a beach here, which seems surprising given most of our west coast beaches in Scotland are filled with sand from the Caribbean, thanks to the Gulf Stream. On our east coast beaches I often spot what we call sea potatoes. I shall keep a look out for any sea dollars, just in case one ever makes it across the ocean in one piece.

    1. A sea potato?! I had to go look that up as I’ve never heard or seen one. I don’t think that they were an item on the beaches of Southern California. but they sure look interesting! There are huge beds of kelp offshore that I think help provide them with their food.

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