SANDDOLLAR MANIA! How many of you have stalked the beaches at low tide in search of everyones favorite, the Sanddollar? What is its singular attraction, and why is it so popular? What can we learn about this animal that takes us beyond its beauty?
Ive just been reading a book by Delta Willis, called The Sanddollar and the Slide Rule, that considers designs in nature and their application to human design, and perhaps improving the human condition. The Sanddollar sets the spin for her story which goes on to tap the thinking of architects and physicists as they look at natural forms and apply them to construction and efficient functioning of man-made structures.
For our purposes in looking at the Sanddollar more closely, I will share some of her ideas and observations, and add a few of my own. We are most likely to find the skeletal remains of this animal on the beach in varying shades of gray, tan and white. A petal design embellishes its upper, slightly domed surface. Ms. Willis describes the surface as an "artists etched blossom with five petals onto thin, delicate sandstone". This design serves as a remnant of 5 rows that accommodated tube feet (used for respiration). The flat underside is pierced with a central hole with 5 radiating channels pointing to the center. Here, you would be looking at the Sanddollars mouth, and may see a few loose teeth peeking out of the opening. Shake it, and the teeth will rattle! If you turn the calcified disc on its edge and rotate, you will find another opening in the otherwise sealed surface. You are now observing the animals anus! Crack open the Sanddollar, and out will fall sand particles and 5 teeth that look like birds in flight. The sand serves as ballast, and the teeth are arranged (in a living animal) into a "chandelier of tendon and teeth" called Aristotles Lantern. You will also observe in the broken shell (called a "test") mineralized supportive struts that give the slightly raised dome strength and shape. Architects take note of this well conformed structure!
If you are walking the beach at a particularly low tide, or after a storm, you may find these animals alive. Their beauty is hidden by brown spines, so the animal looks quite dark and feels rather fuzzy. The spines are longer on the greener undersides, but the mouth is clearly apparent. How does this animal, related to the mobile urchins and sea stars, perform its life functions? The spines, though short, serve to move the animal through its sandy habitat. They help the animal burrow just below the surface. The spines work as sieves directing sand grains into the grooves on the underside that lead to the mouth. Food (detritus and small plants such as diatoms) and sand are ingested. According to Ms. Willis, "sand grains are its currency for diet and stability". The Sanddollars form and function are designed to serve up its dinner of minute food particles and the ingestion of sand which it retains (to a degree) for ballast.
The test is composed of "calcium plates that fit together snugly like the shell of a tortoise", says Ms. Willis. You may have noticed that some of your Sanddollars show these plates more clearly than others. Sometimes, by wetting the surface of a specimen not bleached by the sun, these plates are visible. Look at the plate that surrounds the mouth. It is a complete star, in and of itself. One time, my daughter found just that plate not realizing it was a sea treasure. Later, we realized to what animal it belonged. Putting together these pieces of natures puzzles is part of the fun in beach hunts.
If you have a dissecting microscope, study the live Sanddollar a bit more closely. You will be able to see the spines move and learn that they are "pin striped"! Also, look for the pink tube feet projecting from the surface. These are supposed to have a respiratory function, unlike the mobility function in their family members, the sea stars. If you look carefully, you will see tiny pinchers, called Pedicellaria, that serve to clean the surface and capture foreign matter. Turn the test over and look at its underside. You will notice the spines help orient the sand particles and direct material toward the mouth opening. I looked down at the mouth itself and was reminded of those concealed animal traps with twigs camouflaging a hole. I was not able to see the teeth perhaps if one dissected the live animal, the tooth structure could be observed. As for me, I prefer examining the larger tooth structure of the Sea Urchin, as Aristotle did, so many years ago.
I love to relate the discovery some years ago of the animal that eats Sanddollars. I was filleting a flounder (back when those fish were more numerous) and carelessly punctured the fishs stomach with my knife. Out popped dozens of tiny Sanddollars! I always like to think of flounder, and other bottom feeding fish, probing the sand for small, round, "cookies"!
So how do you respond to finding a Sanddollar? Do you look at its shape and start designing flying saucers? Ms. Willis related that scientists look at the animal and call it "extreme, aberrant and mysterious". Another naturalist called the echinoderm family a "noble group especially designed to puzzle the zoologist". Others see religious symbols in its design. Still others find the discs a good luck piece. To all it is a treasure worth seeking and understanding.
11/21/98 Ronnie K.