Lower Section of Sponge
An illustration of the lower portion of a sponge. O, OS, and M are illustrations of sponge eggs magnified forty times. The sponges or poriferans (from Latin porus "pore" and ferre "to bear") are animals of the phylum Porifera. Their bodies consist of an outer thin layer of cells, the pinacoderm and an inner mass of cells and skeletal elements, the choanoderm. Sponges do not have nervous, digestive or circulatory systems. Instead most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, and the shapes of their bodies are adapted to maximize the efficiency of the water flow.