Water enters the sponge body through holes in the tissue called ostea, moves into choanocyte chambers, and then is moved through the body by the canals until it exits through a chimney-like osculum (Simpson, 1984 Manconi and Pronzato, 2002). They have ciliated cells that function to move the water to the channels that run through their bodies. Sponges are filter feeders, and move water through their bodies so that they can absorb particles in the water column to eat. As basal animals, sponges do not have true developmental tissue layers although they do have 11 different cell types, some of which may function together (Simpson, 1984 Manconi and Pronzato, 2002). This makes sponges the most basal extant animal species and an excellent candidate for looking at the evolutionary conservation of ancient genes in animals. Freshwater and marine sponges are members of the phylum Porifera, which split off of the animal lineage before the Cnidarian and the Bilaterian split (Peterson and Davidson, 2000).
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