The sponges are multicellular animals but they do not form tissues. They have aggregated cells body plan. Thus, they do not have organs, such as the mouth. Sponges are the members of Porifera which means they are pore-bearing animals. Their body is covered with tiny pores (ostia) which lead to a canals system. Within the canals, chambers are lined with special cells called collar cells (choanocytes). The collar cells have sticky collars which engulf tiny bits of food that brought with the water. Digestion takes place within the cells by enzymes secreted from lysosomes.
