 The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where the water deposits nutrients and then leaves through a hole called the osculum.Many sponges have internal skeletons of spongin and/or spicules (skeletal-like fragments) of calcium carbonate or silicon dioxide.All sponges are sessile aquatic animals, meaning that they attach to an underwater surface and remain fixed in place (i.e., do not travel).