Painting of a sponge by Dr M. Ramult, Curator of the collections in the 1950s.
As the painting shows, sponges are constructed around a series of canals and chambers supported by minerals secreted in the form of needles or multi-rayed spicules. The outer surface is covered with flattened cells. The middle layer is a gelatinous matrix containing the spicules. The inner lining of the body cavity is lined with choanocytes. Sponges feed by filtering a stream of water through porocytes embedded in the body wall. The water is taken by choanocytes beating their flagellae. The collars of these cells filter out small organisms and nutrients from the water. The water is ejected through the main opening or osculum.