The Pacific Ocean sparkles under the new morning sun on this Memorial Day weekend. The fierce waves of yesterday have receded, leaving the beach littered with bits of broken shells and rocks, abalone shells and sand dollars. I found a large group of sand dollars here in this spot on Pismo Beach. Sand dollars are not strewn evenly across the beach, I have observed, but seem to be found all together in certain spots, and then nothing for a long while. Some of the sand dollars were intact, displaying a 5 pointed symmetrical design (petal-like design) on their perfect white coin-shaped shells, while others were broken, either stepped on or crushed by last night’s fierce waves.
I walked closer to the water enjoying the low tide and the opportunities it might afford me. There, between the low tide and high tide lines I spied a different sand dollar than the ones I had seen before. This one was not white, but purple. When I stooped to touch it, I realized it was still alive! All of the other sand dollars had been hard skeletons, bleached white by the sun. This purple one had legs!
I couldn’t believe my eyes, but he was moving.. walking in fact, very slowly. Oh, why did I go out without my camera today, or better yet the camera phone that takes movies? I am sharing a YouTube Video here of a sand dollar walking since I wasn’t able to record one myself. This is a Time Lapse Video of a Walking Sand Dollar from Pismo Beach, California!
Of course, I let him be, just watching the living sand dollar for a time, until he buried himself in the sand. Whether he wanted to hide from me or to find a meal, I am not sure. Hope he is careful not to get stepped on!
Until I saw the sand dollar walk, I had thought perhaps a sand dollar was a fossilized plant, rather than an animal. Further research was needed.
I learned that Sand Dollars are hard-skinned animals called echinoderms (which means “spiny skin”) and are related to sea urchins and sea stars (or star fish). Wikipedia has them belonging to the order Clypeasteroida.
The sand dollars live on the sandy sea floor, from the intertidal zone (the area between high tide and low tide) down to the subtidal zone (the area below low tide). Sand dollars are usually crowded together over an area—as many as 625 sand dollars can live in one square yard
The sand dollars are covered in soft “spines” which help it move across the seabed. Unlike the hard top of the sand dollar, the underside is soft with moving “cilia” which the animal uses to catch food, such as tiny shrimp. These cilia sweep the food up to the mouth, which is a hole in the center of the flat coin-shaped animal. It amazed me to learn that these creatures have mouths, because when I look at it I see nothing. But on closer inspection, you will see a hole on the underside. If you don’t see a hole, it is because it is still alive (the cilia are covering it) and you should put it back right away! In fact, in some places sand dollars are protected and it is illegal to take them from the beach.
Sand dollars are very fragile. If they are in quiet waters, they have the ability to stand “on end” or partially bury in the sand. When waters are rough, sand dollars hold their ground by lying flat—or burrowing under. If the waters are fast moving, the adults are able to build a tougher skeleton to fight the currents. The young sand dollars drink in sand to hold themselves down. In contrast, the baby Sand Dollars (larvae) are swept along by ocean currents and travel many miles.
The rigid skeletons of the sand dollars are called “tests” If you were to break open a test, you would see many hard, loose, white pieces; these were the teeth of the Sand Dollar used to chew up their food.
I walked back down the beach, marveling at all of the wildlife of the sea, right underneath our feet, and we don’t even know what most of it is. I wonder how many of these living sand dollars I have seen before and just passed them by because, half-buried, you can’t tell the living ones from the dead ones.
On this holiday weekend, I find myself left with more questions than answers about the wildlife treasures the sea might hold.
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