Dennis Lindberge, age 15, of Garden Grove, California, for his question:

How do sponges move?

Many people go through their whole lives thinking that a sponge is a plant. After all, it looks like a low growing bush and we have to pull it loose from its fixed spot on the floor of the sea. But actually, of course, it is an animal. It is an animal that has no heart or blood, no lungs or gills, no head or mouth, no nervous system and no legs. With all this lack of equipment, we cannot expect the underprivi¬leged fellow to perform many antics. An adult sponge spends its entire life fixed to one spot. It could not move to another spot if it tried. As an infant, it spent a short time floating around freely in the water. But the sea is a hungry place and full of hazards. If the infant sponge is lucky enough to survive it soon settles on a solid spot and stays there.

The life of a sponge seems rather stodgy, but some 3,000 species manage to survive in the waters of the world. They are classified in the Phylum Porifera, the pore¬ bearers. Their bodies are riddled with pores and tunnels. Water, carrying food and oxygen, streams through these pores to keep the sedentary sponges alive.