Every day, everyone uses some kind of sponge to wash their dishes or their cars. We usually use inexpensive sponges made in factories from synthetic materials. However, people might never have thought about making sponges if animal sponges did not exist.
Sponges live under water. Most sponges live in salt water. The 5,000 species of sponge belong to the Phylum Porifora. They are further classified into four groups based on what comprises their skeletons. Calcarea sponges have limestone skeletons. Hexactinellida have skeletons made of silica. (Since glass is made from silica, these sponges are nicknamed "glass sponges." ) Sclerospongiae have a combination skeleton of both limestone and silica. Finally, the fourth class of sponges are the demospongiae, which live in fresh water.
A wide variety of sponges exist, ranging in size from 1 inch to 4 feet in diameter. Inside a sponge there is a system of openings and passages called a canal system. The sponge is nourished by chemicals that they filter out of the sea water passing in and out of these canals. Mature sponges do not move around. After the larvae separate from their parent's body, they find a place to attach themselves to the bottom of the ocean or river where they will remain for the rest of their life. Sponges can live for a very long time; in fact, scientists think that some live sponges could be as many as 5,000 years old.
The life cycle of sponges involve two kinds of reproduction. During asexual reproduction, the sponge develops buds which break off of the parent sponge. The buds then become mature new sponges. This happens because of a special kind of cell called an archaeocyte. The archaeocyte becomes surrounded and protected by another kind of cell until the conditions are good for a new sponge to develop. Then the archaeocyte "hatches" and develops into a new mature sponge. The other kind of reproduction that sponges use is sexual. Interestingly, a single sponge may have both male and female reproductive cells.
Sexual reproduction in sponges starts when an egg begins to develop inside the parent's body, fed by the fluids that flow through the parent's canal system. Special cells called "nurse cells" gather around the egg to make sure that it gets enough nourishment until it is mature enough to be fertilized by a sperm. Sperm cells can be produced by the same parent that produced the egg, right in the same body. They can also be released into the water by a male sponge that lives close to the sponge that contains the mature egg. This sperm enters the female through the openings in her canal system known as ostias. After the sperm and egg cells combine, a larva develops. This creature is covered by hair-like flagella that allow it to move and swim right out of its parent's body. Once the larva attaches to something on the floor of the ocean or on the bottom of a fresh water area, it will stay there and grow until it is an adult.
Sponges eat while they filter the water in which they live. They can pump in and out a volume of water that is equal to ten times their weight. This does not just nourish the sponge. The sponge serves the environment by filtering out, cleaning, and digesting the toxins that other animals and plants deposit into the water. Some of the chemicals are turned into other substances which help the sponge defend itself against being eaten. This also makes some of the sponges toxic to humans, however, scientists think that sponges may produce substances that could help treat cancer and other human diseases.
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