Although there are over 5000 different types of sponges residing in the world, they each share similar characteristics. Sponges have a system of pores (also known as ostia) and canals which allows water to pass through freely. This water carries nutrients and oxygen which is vital for the sponge to live. Water also helps waste products to flow out. The movement of the water is initiated by flagellae which are found on special cells known as collar cells.
Sponges can be radially symmetrical or asymmetrical depending on simply their shape. They are held up by a skeleton made up of the protein collagen and spicules. Skeletal elements, choanocytes, and other cells can be found in a jelly like matrix called mesohyl (also known as mesoglea). Sponges have the least complex kind of cellular organization found within parazoans.
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