Porifera are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them.
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Sponges are apart of the Porifera phylum. With over 5,000 species, 150 are fresh water, the rest being marine. A sponge excretes waste substances the same way it takes in food and breathes. The water flows through the sponge's pores and filters out the waste Once the water flows through the pores, the excretion (along with carbon dioxide) exits out through those pores.