Osculum

The osculum is an excretory structure in the living sponge, a large opening to the outside through which the current of water exits after passing through the spongocoel. Wastes diffuse into the water and the water exits through the osculum at a velocity of nearly 8.4 cm/second, carrying away with it the sponge's wastes. The size of the osculum is regulated by the myocyte. Its size, in turn, determines the amount of water flowing through the sponge.