Sponges Sponges Sponges are the simplest of the multicellular animals. They have no organ systems and are characterized by numerous canals and chambers that open to the outside by way of pores which giving this phylum its name.
Many sponges are asymmetrical, but some exhibit radial symmetry.
They are almost plant-like in their simplicity and are often confused as being plants. The body plan of a typical sponge is shown in figure1. The ostia are surrounded by donut-shaped cells called porocytes that open and close to control water flow. General body plan of a simple sponge. The choanocytes have a tubular collar facing the spongocoel.