CHOANOCYTE

'Choanocytes' (also known as "collar cells") are cells that line the spongocoel of sponges that contain a central flagellum surrounded by a collar of microvilli. It is the closest family member to the free-living ancestor called choanoflagellate. The flagellum beats regularly, creating a water flow across the microvilli which can then filter nutrients and other food from the water taken from the collar of the sponge. Food particles are then phagocytosed by the cell...
By lining the walls of spongocoel, they create an intracellular space called the porocyte.