Choanocytes or collar cells line the spongocoel and the canals. The collar cells have a sticky, funnel shaped collar and a hairlike whip, called a flagellum. The collar cells serve two purposes. First, they beat their flagella back and forth to force water through the sponge. The water brings in nutrients and oxygen, while it carries out waste and carbon dioxide. Second, the sticky collars of the collar cells pick up tiny bits of food brought in with the water. Another type of cell, called an amebocyte, takes the food to other cells within the sponge.