Rosslynne Sullivan, age 14, of San Diego, Calif., for her question:
HOW DO SPONGES EAT?
It wasn't too long ago that people thought sponges were plants. They found them anchored at the bottom of oceans, and they didn't move around. And it seemed very natural to think they could be a type of plant. But zoologists say they are animals and indeed they are. They belong to the animal phylum called Porifea which means pore bearers. They're covered with tiny pores.
Sponges can be found in both shallow and deep water. Although they call most oceans home, they are found mainly in warm, tropical waters.
There's no other animal that looks or acts like a sponge. He has no head, mouth or internal organs. And he eats in a most interesting way. His entire body is made up of a system of water canals and it is through this network that he receives his food and oxygen. This system is also used to carry away waste products.
On the sponge's surface are tiny pores which lead to the tiny canals. Food and oxygen enter the body through the pores and then are carried through the canals into small chambers. These spaces are called flagellated chambers because each cell that lines them contains a long thread that whips around to aid movement.
A sponge's flagellated chambers drain to other tiny canals. These in turn join a network which eventually lead to the outside through a large opening in the sponge's body called the osculum. Thousands of flagellated chambers and canals can be found in a piece of sponge that is no larger than a marble.
Some sponges are vase shaped and have only one osculum. Others that are not symmetrical have many oscula, each providing an exit from the thousands upon thousands of flagellated chambers and canals. Many scientists believe that a sponge with many oscula is not a single animal but a colony made up of many sponges.
Water flows through a sponge, and as it does it sweeps tiny plants and animals through its body. Food particles in the flagellated chambers are actually engulfed and digested by the sponge.
Sponges have several kinds of skeletons. Some are made of tiny needle like rods called spicules. Others are made of fibers called spongin, while still others have skeletons that consist of both spicules and spongin.
A sponge begins his life as a single cell, an egg. The egg divides inside the body of the parent and keeps dividing until it forms a tiny larva covered with flagellated cells. Then the water circulating through the parent's body sweeps the larva outside the body and the tiny creature is on its own.
The tiny larva beats and lashes its flagella as it moves through the water until it finally attaches itself to a hard surface.