The correct option is C choanocytes
The body of sponges (poriferans) has several minute pores called ostia through which the water enters into the central cavity, spongocoel.
The flagellated cells called choanocytes (collar cells) line the spongocoel. These cells generate a flow of water and the water current helps in food gathering, respiratory exchange and removal of waste.
The water finally goes out of the body through a large pore called osculum. (Plural: oscula).
The body wall of the sponge is composed of two layers: outer pinacoderm and inner choanoderm. In between these two layers, mesenchyme is present with various mesenchymal cells.