What is the function of collar cells in sponges?

Collar cells beat their flagella back and forth to force water through the sponge. Collar cells also pick up tiny bits of food brought in with water.

Sponges are covered with tiny pores that are called ostia, which lead to a system of internal canals. The canals eventually lead to one or more larger holes that are called oscula. The canals of sponges have chambers lined with collar cells. Collar cells have a sticky funnel-shaped collar and a hair-like whip that is called the flagellum. A cell called an amebocyte takes the food picked up by a collar cell to other cells within the sponge. Collar cells are also called choanocytes.