Sponges are considered very basic, not having many animal characteristics. Sponges only move around when they are young and small, when they are larvae. They then land on a piece of rock reef, and are permanently anchored or rooted. Most are found in seawater, as opposed to freshwater. They don't have tissues, or a nervous system. Sponges contain pores, called ostila, through which large amounts of water circulate. The water is used as a source for nutrients & oxygen, and also carries out waste. They are known as filter feeders, since they filter food from the water that passes through their body. Sponges lack tissues, instead having several special cell types that perform specific functions. They are able to produce sexually and asexually. The size of a sponge is limited by it's ability to circulate water through it's body. During the evolution of sponges, the problem of water flow was overcome by folding the body wall, and reducing the size of the sponge. In our ecosystem, sponges lower nitrogen levels in water and keep the ecosystem clean.
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