There are different types of cells presents in sponges. The gastral layer of sponge contains a special type of cells called as choanocyte cells. These are also called flagellated cells.
Each cell is big. It is oval in shape. It has a big nucleus. It shows contractile vacuole and food vacuole. From a basal granule a flagellum arises. At the base of the flagellum a protoplasmic collar is present. Hence it is also collar cell.
In Sycon, these cells are restricted to radial canals. They are called flagellated chambers. By the action of flagelia water current is brought in. The incurrent water brings in food particles and 02. These food particles are filtered by the collar of the choanocyte. These food particles may be digested by the choanocyte or may be given to the amoebocyte.