They have no true tissues or organs, rather various individual cells perform the life functions of the sponge. This matrix is what remains behind when sponges are found on the beach or prepared and sold for market. The living part of the sponge exists within this matrix. Water enters the sponge through many pores, and is helped along by specialized cells which sweep the water through interior chambers and canals. The water circulating through the sponge supplies oxygen and food, and removes wastes as well.
Sponges pump a surprising amount of water in a day.
Sponges eat very fine detritus particles and organisms such as bacteria and plankton. Sponge beds provide a significant amount of habitat for other animals, and they also may be responsible for filtering, i.e., cleansing, vast quantities of water in given areas. These animals, along with the less familiar hydrozoans, belong to the phylum Cnidaria. They are the first group of animals to display differentiated tissues, limited organ development, and nerve cells. They possess an internal digestive cavity and a mouth, which permit a greater range of food sizes than exists with the sponges.