<P> Choanocytes (also known as "collar cells") are cells that line the interior of asconoid, syconoid and leuconoid body type sponges that contain a central flagellum, or undulipodia, surrounded by a collar of microvilli which are connected by a thin membrane . They make up Choanoderm, a type of cell layer found in sponges . The cell has the closest resemblance to the choanoflagellates which are the closest related single celled protists to the animal kingdom (metazoans). The flagellae beat regularly, creating a water flow across the microvilli which can then filter nutrients from the water taken from the collar of the sponge . Food particles are then phagocytosed by the cell . </P> <P> Choanocytes are found dotting the surface of the spongocoel in asconoid sponges and the radial canals in syconoid sponges, but they comprise entirely the chambers in leuconoid sponges . </P> <P> By cooperatively moving their flagella, choanocytes generate a flow of water through the sponges pores, into the spongocoel, and out through the osculum . This improves both respiratory and digestive functions for the sponge, pulling in oxygen and nutrients and allowing a rapid expulsion of carbon dioxide and other waste products . Although all cells in a sponge are capable of living on their own, choanocytes carry out most of the sponge's ingestion, passing digested materials to the amoebocytes for delivery to other cells . </P> <P> Choanocytes can also turn into spermatocytes when needed for sexual reproduction, due to the lack of reproductive organs in sponges (amoebocytes become the oocytes). </P>

What does the choanocyte do in a sponge
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