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In this image, a florescent dye has been injected next to a sea sponge which the sponge quickly pumps through its body. Sponges don't have tissues or organs. The beating choanocyte cells (specialized cells with flagellae) and the porous structure of a sponge s body are specialized to pump water--thousands of liters a day--throughout its body, extracting tiny organisms for food from the water to all the cells.
Image credit: ©2002 Sea Studios Foundation
