Annette Heigle, age 14, of Forest Grove, Ore . , for her question:
Is a starfish rally a fish?
A scientist must be very orderly in his work and very exact when he talks about it. If he used the wrong name for an animal, other scientists would fail to understand him. For this reason, many experts would me to award the cute little starfish another name. True, the little fellow often is shaped like a star, but he is certainly not a fish.
In everyday language, he has been called a starfish for countless generations. His name has become a habit with us, and it would be hard to change it. But many experts would like us to call the spiky little animal a sea star. This is a suitable name for he lives in the sea and is shaped like a star. But not one of the more than 1000 species of starfish is related to any of the true fishes.
The so called starfish belong in the phylum echinodermata, the spiny skinned animals. The echinoderms are further divided into five classes. In everyday language, we have misnamed not only the starfish, but also his cousins in the four other classes of his phylum.
One class of echinoderms includes the serpent stars, which are not remotely related to the snakes. Another class includes the Sea cucucumbers, chunky fellows that are not even plants. Another class of echinoderms includes the graceful sea lilies, which are not flowers. An urchin is a mischievous boy, but the echinoderm class of sea urchins is not related to the human race.
The starfish belongs in the class Asteroidea, the star shaped animals. His starry little body is a flat disk surrounded by tapering fingers. Like all echinoderms, his body is built on a five sided plan. If he has five fingers, you can see his pentagon design clearly. He may have 10 or more fingers, in which case his five sidedness is not so plain to see.
An echinoderm digests his food in a central cavity called the coelom. The mouth of the starfish is a hole on the underside of his body. Instead of a pair of fish¬type gills, he has many small skin gills. Water enters through these small openings, and oxygen is removed by fluids in the coelom.
The starfish feeds on oysters, clams and mussels. His fingers have rows of powerful suction cups. When he is hungry, he grips the two shells of, say, an oyster and pulls. The stubborn oyster refuses to open, but the steady pressure soon becomes too much for him. He relaxes his muscles, and the starfish pries open the shells to get at the tender meat inside.