Denise Koeppe, age 11, of Omaha, Nebraska, for her question:

What is a live sand dollar like?

In summer we visit the beaches, where the cool bright waves toss tangy salt spray in our faces. We prance along at the water’s edge, where the sea washes up shells and all sorts of other secret items from below the water. For example, that small bony pancake thing is called a sand dollar. Actually it is all that remains of a long gone sand dollar, who looked very different when he was alive.

When living, the average sand dollar resembles a three or four inch pancake, made of black or purple velvet. In the center, there is a neat, five petal flowery design. However, we rarely get to see a living sand dollar because the timid creature buries his little body in the sand, usually just below the lowest low tide. Most of the many species prefer warmish waters, though one lives as far north as Alaska.

The various sand dollars are echinoderms, or prickly skinned animals, related to the sea urchins and starfishes. Most of the earth’s animals have two sided bodies with a head end and a tail end. The amazing echino¬derms have five sided bodies. This design is seen in the five armed starfish and in the five petal pattern on the sand dollar.

The sand dollar’s remarkable skin is covered with velvety threads about one sixteenth of an inch long. The numerous mini hairs are covered with mucous to trap floating fragments of food. Small helpings of fish or seaweed, alive or dead, are acceptable. The tiny hairs wave them along well worn channels to the sand dollar’s mouth, which is a small round hole in the center of his under side.

Streams of water flow through his simple internal organs, bringing dissolved oxygen and removing waste carbon dioxide. His soft insides are held in shape by a limy round skeleton, which is re enforced with tiny rods. The so called sand dollar we find on the beach is this pancake shaped skeleton, from which the skin and internal organs have decayed and been washed away—possibly to feed other sea dwellers.

Since the sand dollar’s five sided design is so remarkable, one would expect him to wear this model all his life. Not at all. Life begins when adult sand dollars strew male and female cells into the water.  When    a pair of cells meet, they merge to form a fertilized egg and the miraculous process of a new life begins. The egg cell. divides and divides again and again—until the embryo becomes .an infant sand dollar larva.

This little fellow is a born swimmer. What’s more, he has a definite head and tail end with two opposite sides. During this phase of his life, the sand dollar is a two sided animal. Later, he gives up his hazardous free swimming life and sinks to the bottom. There his body goes through a drastic remodeling. The result is a flat, five sided body—just like the flat, five sided bodies of his parents.