How do sponges feed if they cannot move?

As the flagellae of the cells inside the sponge beat the water, a current is set up and water is drawn through the tiny pores into the center of the sponge and then driven out through the hole at the top. Suspended particles of food in the water are caught on the flagellae of the cells and passed back to the amoeba like cells. Another function of these cells is to absord the food particles filtered from the water and to transport the digested food to the other parts of the sponge. The cells bearing flagellae can only deal with a certain size of food particle, and so no matter how large the sponge, it must feed on microscopic particles such as bacteria and protozoans suspended in the water.