Raymond McGuire, age 11, of Winnipeg, Man., Canada, for his question:
IS IT TRUE THAT THE SPONGE IS AN ANIMAL?
If we judge by appearances, most of us would classify a living sponge as a plant. It squats there on the ocean floor, looking for all the world like a chubby little bush. However, scientists who classify the plant and animal kingdoms are not fooled by appearances. And they assure us that the sponge is an animal.
The sponge we know best is the one we use in the bathtub. It is a fistful of squeeze able material, eager to froth up a soapy lather and just right for scrubbing the dirt from human skin. However, it is merely the skeleton of a real live sponge that spent his lazy life squatting on the floor of a salty sea.
The skeleton of a living bath sponge is padded with fleshy tissue and covered with a thick leathery skin, often tinged with purple. Without a doubt, it is an animal, though one of the strangest animals that belongs to the planet earth. Along with some 3,000 close relatives, it is classified in the phylum porifera, which means the pore bearers.
The so called pores are tunnels that riddle the skeleton bath sponge. During its lifetime, these tunnels formed a network through the tissue and made porous openings in the skin. Streams of water ran through the system of tunnels and out again. The water carried dissolved oxygen and fragments of food, which were used and digested by cells in the tissue.
The sponge multiplied by producing male and female cells inside its body. The male cells escaped into the water. A few managed to enter other sponges and fertilize the female cells that stayed home. The fertilized eggs took to the water as larvas and enjoyed a day or so of freedom.
However, when the immature larvas were about as big as pinheads, they sank down and settled themselves on solid surfaces. There they spent the rest of their lazy lives, while streams of water served free food and oxygen through their pores. Recent studies suggest that a young sponge may move to more suitable quarters. However, his top speed is about one inch in two weeks.
After about seven years, the lazy sponge animal is big enough to be gathered, stripped down to his skeleton and sent to market. If left in the sea, he may live as long as 20 years or so. By this time the chunky fellow is about 20 inches wide. If his body is cut into several pieces, each piece can rejuvenate and grow into a new sponge.