The Barrel Sponge is under the porifera animal phylum and they got their name because they are big, and shaped like a barrel. Some barrel sponges grow to a size where a human being can actually fit inside of it. The barrel sponge has a hard surface, and a delicate, flimsy rim. This type of sponge belongs to the Demospongiae class of sponges. This group is actually 95% of the species of sponges. The barrel sponge is usually found in the colors red, brown, gray, and purple. The barrel sponge is commonly known as the giant barrel sponge because its barrel can reach a diamater of 2 meters, while their sponges can usually grow about 1.5 centimeters a year. This sponge is so big that it provides habitat for fish and invertebrate species. Perhaps the most important feature, however, of the barrel sponge is that its sea-water filtering capacity is one of the largest among the sponge species. This makes the barrel sponge a great interest to scientists, and also very important.