Ronald Maddeaux, age 12, of Tucson, Ariz., for his question:
Is it true that sponges grow underwater?
The squeezable sponges, riddled with pores and tiny tunnels, have been mankind's faithful washers and scrubbers since ancient times. The age of science has brought us many imitations made of foamy plastics, and these almost as good sponges are man made on dry land. But all the world's natural sponges do their slow and patient growing underwater.
The 3,000 or so different sponges are classified in the phylum porifera, meaning the pore-bearers. Most of them live their lazy lives in warm, shallow seas, though a few of the smaller varieties grow in the fresh waters of lakes and rivers. The largest of the pore bearers may be three feet wide and the smallest no bigger than pin heads. They come in a wide assortment of shapes and colors, and growing in their natural surroundings they could be mistaken for underwater gardens of small shrubs and humped bushes, lacy flowers and blossoms.
For a short period in infancy a sponge may be a free swimming larva near the warm surface of the sea. But most of its life is spent firmly anchored to a rock or on the solid floor of the ocean. It may be fixed to a floating log or to the wood piling of a pier. But every sponge must live and do its growing underwater. Its simple body is built for life in the water and soon perishes in the dry air.
Even the experts once thought the sponges belonged in the world of plants. They have no heads or hearts, no arms or legs, no nervous or blood systems. Adult sponges cannot move about like most other members of the animal kingdom. Nevertheless, they are animals. Water circulates through their tunnels carrying algae, small sea dwellers and fragments of decaying plants and animals. These scraps of solid food are digested and waste materials returned to the water. Oxygen also is taken from the water circulating through the pores.
The fleshy body of the sponge is built around a durable skeleton made from minerals taken from the water. The skeleton is riddled with tunnels, and it may be made from chalky calcium chemicals or from hard and glassy silica. A few sponges have skeletons made of soft spongin, a material very much like our hair and nails. The skeletons of these spongin sponges are the sponges we use to help us with cleaning and scrubbing jobs.
Most of our natural sponges are gathered from the balmy waters off the coast of Florida. Other favorite spots for spongin sponges are in the warm Mediterranean off the shores of Greece, Italy and Sicily. The living sponges are cut and brought up by divers and left to dry in the sun until the flesh can be removed from the spongy skeletons. The sponges are then cleaned, trimmed and graded and sent to market.