Dorothy Jensen, age 12, of Staten Island: New York for her question:
When did the starfish originate?
His family tree dates back more than half a billion years. His original ancestors lived in the fresh waters of the ocean during the Cambrian Era of the earth's history.
In outward appearance they were quite different from our modern starfish, but they had basic family features that have not changed through the ages. Neither have any of their descendants forsaken the'home of their ancestors. There are 8,000 or so living species and all these starfish still live in the sea.
The modern starfish is classified in the Phylum Echinodermata the spiny skinned ones. Most echinoderms have spiny or bumpy skins and those that appear smooth have small calcareous plates embedded in their coats. So do many other animals. But the echinoderms have a couple of features that make them unique. Each has a water¬vascular system throughout his body that leads to a multitude of tube feet. And each has a body supported by a ring of rays, arranged like the spokes of a wheel spreading out from a central axis.
These basic features identify the starfish and his kinfolk. For almost all the other creatures of the earth have bilateral; two sided bodies. ~A starfish may have 5 to SO arms, but his body structure is shaped like a sunburst. This feature identifies the fossils of his original ancestors. They are called cystoids and they shared the ancient Cambrian seas with other echinoderms, plus a multitude of crusty trilobites. This was at least 500 million years ago, ages before any plants or animals ventured from the water to live on the land.
Compared with the modern starfish, their cystoid ancestors were very simplified creatures. They had no separate, tapered arms. But they had five grooved feeding tubes arranged in a radial pattern. In this form they survived more than 130 million years. The last cystoid fossils were left behind in the Carboniferous Period, when a few animals and whole forests of green plants were established on the land.
However, the starfish family tree did not perish. It was carried on by more advanced echinoderms called crinoids. These ancient creatures had branching arms but still no tube feet. Long before the ancestral cystoids became extinct, the crinoids gave rise to a branch of the family that finally led to the starfish. This was during the Silurian Period, some 350 million years ago. The first recognizable starfish made their appearance about the same time that a few bold scorpions left the ancient cradle of the sea and became the first animals to cope with life on the dry land.
The echinoderm starfish, of course, is in no way related to the true fishes. Some scientists insist that he should have a more suitable name that does not confuse him with the fishes. They suggested the name sea star. After all, he does belong to the sea and whether he has five or 50 arms, his amazing little body is shaped like a star.