They are asymmetrical in nature, and are nothing much more than an assemblage of cells.
Sponges have no tissue, but they do have specialized cells.
Some of the specialized structures would be the incurrent canals which are lined with porocytes. The choanocytes line the flagellated canals. Sponogocoel makes up the central chamber. The opening used to expel water is called the osculum. Finally, the amoebocytes secrete skeletal fibers.