Patty Jacobson, Age 12, Of Rockford, Ill., for her question:

How many animal species are there?

We know of about one million different animal species, and more are being identified all the time. Most of the sizable backboned animals are known and accounted for. But these vertebrate species number only about 500,000 or 5% of all the different animals in the world.

Among the invertebrates, we know of more than a half a million insects, and far more are waiting to be identified. The sea swarms with animals that do not even walk around, such as oysters and sea anemones, clams and sponges. The land and oceans teem with uncounted one cel1ed animals too small for our eyes to see. The million or so animal species we know are but a small fraction of all the different animals that share our planet.