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Sponges

What is a sponge? Is it the soft squishy thing you use to clean things? Is it the poofy lufa you use in the shower? Or is it something much more unique and interesting? To learn the facts about sponges, keep on reading.

Scientists believe that sponges were the first animals to be alive. The ancestors of today's sponges were alive billions of years ago. Sponges have looked the same for millions of years. They are the most simple of all animals, with no brain or organs, but they have been helping mankind and nature for as long as they have been on the planet.

Sponge is a simple word used to discuss these animals. Sponges are known by scientists as porifera. In Latin, this means "pore-bearing." The pores, or tiny holes, in the skin of a sponge water in so that the sponge can extract oxygen and food for all of its cells to stay alive. The water passes by the mesohyl, also called the mesenchyme which contains cells and the sclerocytes. Sclerocytes make spicules. After the water is filtered, it is pushed out of the sponge. First it goes to a hollow area called the spongocoel, which is a large, empty cavity. Sponges contain one large hole at the top of their bodies, known as an osculum, and they also have smaller holes on the sides known as ostia. With so much water flowing in and out of a sponge every day, sponges in the Caribbean Sea can filter the entire sea in just one day. That's pretty impressive for an animal that was thought to be a plant until the year 1765!!!

Sponges may seem to be plants, but they are really just primitve, simple animals. They are not animals like humans because they only have cells. Cells are the tiniest parts of the body, and you can't even see them. Each cell in a sponge has a special job, and when cells of the same type come together, they make tissues. Tissues create organs, but sponges don't have any organs. That means no brain, eyes, hearts, etc. However, despite all that is set against them, they always manage to stick together. While their spicules, tiny needles that stick out from the sponge, hold them together, sponges also have another special way to stick together. If you had a sponge in a salt-water aquarium and break it up into thousands of pieces, the cells would come back together again in the exact same shape within several hours. You definitely can't do that to humans! However, let's discuss sponges a little more in detail. 

We'll start on the outside. Spicules, the needles that stick out, are on all sides of the sponges. They are both bristly and sharp. Not only do spicules hold the sponge up, but they also protect it from predators. Only a few animals eat sponges because they have a bad taste and chemicals that are toxic to other creatures.

Covering the sponge is a layer of cells, very similar to skin, but it's slightly different. To scientists, these cells are known as pinacocytes. In a sponge, pinacocutes are a thin, elastic layer which keeps too much water out of the sponge. Between the pinacocytes, there are the porocytes. These let water into the sponge. Myocytes, little muscular cells, open up the porocytes and close them. Once through the pores, water travels down canals. Using the food and oxygen inside of the water the sponge cells stay alive and carry out other processes such as making new sponges and repairing cells. In addition, there are other organisms that live inside a sponge. One very large sponge was once found to have 17,000 other organisms living inside of it!

How does the sponge take all the food and oxygen out of the water? Oxygen is absorbed right into the cells. But the food is a different issue. Special cells help to take the food out of the water. These are the choanocytes. Each choanocyte has a collar which takes the food and a flagellum, or little whip. The whip catches the food as it sways with the water. Then, archaeocytes (the best cells in the sponge that do everything from transport food to make new sponges) come and take it to other sponge cells. After this, water is pushed into the spongocoel and out of the osculum or ostia.

There are all types of different sponges. One way that scientists describe sponges is to look at how they are built. There are three main types of ways that sponges can be built.

Asconoids -These are the simplest of the sponges. Usually, they come from sponges that lived long ago. They are about 4 inches or 10 cm. Also, they usually look like a slender sack or tube.
Syconides -In comparison to asconoids, these are slightly larger, thicker, and more complex. Their holes make rows on a smooth surface. Also, they are shaped like tubes.
Leuconides -Leuconides are the largest of all the sponges. They are the best constructed for movement. In five minutes, they filter their own weight in water.

Sponges take up an entire phylum for several reasons. First, there are more than five thousand different types of sponges. Second, they are different from all other animals. Third, their history does not link them to other animals.

Usually, sponges are grouped into three classes known as the Demosponges, Calcarea, and Hexactinellida. When new tests are conducted, scientists may take a species or even an entire order out of one class and move it to another. There was once a fourth class of sponge (known as Sclerospongiae). However, it was dissolved, and the sponges within it were either moved to a different class or put into a new phylum. Some scientists even have a theory that the Hexactinellida should be a new phylum called "Symplasma".

Demosponges are the biggest group of sponges. Demosponges are the only group that has freshwater members. Only 5% of all sponges can live in freshwater. The other 95% live in salt water bodies such as oceans and seas. Most of the demosponges are more complicated than the other sponges. They are members of the Leucon grade, which means that they have many canals inside their body and their shape can change throughout the day to take in more water. By studying the fossil record, it appears that demosponges were not so common long ago as they are today. During the Cretaceous period, when there were lots and lots of sponges, demosponges were only half of all the sponges. But this could be so because demosponge spicules are made of silica. Spicules are tiny needles that grow from the inside to the outside of the sponge, and they provide protection and structure for the sponge. Since the demosponge spicules are made of a less strong material, when the the bodies decomposed, their spicules could have easily dissolved.

Calcareous sponges have spicules made of calcium carbonate. These spicules form rays and circles as they come out of the skin of the sponge. Their surfaces may be pastel colors as well as tan and black. If you were to see a calcareous sponge, it could be a pear or a purse shape. Also, it would look kind of bristly because of its spicules. There are over 100 different genuses of calcareous sponges. In the world, they usually live in tropical waters less than 1000 feet deep, but they have been found at far deeper depths.

Hexactinellids are very interesting sponges. Of all the sponges, they are thought to be the most beautiful. As is suggested by their name, hexactinellids have six points. They look a lot like stars. Many hexactinellids are called "glass sponges." Hexactinellids were the first group of sponges to develop, but as said before, many scientists do not believe that they are sponges at all. Oddly enough, they have electric receivers on their spicules which can conduct electricity!