A body form of medium complexity in sponges where the body wall has become folded and the choanocytes (flagellated collar cells) are not located along the spongocoel, but along radial canals. Water enters the sponge through a series of incurrent canals and passes through internal pores called prosopyles into the radial canals, which are lined with flagellated choanocytes.- It is the action of these choanocytes that keeps water moving through the sponge. From the radial canals, water then enters the central spongocoel through pores called apopyles, to exit to the environment through a single opening, the osculum.