An Introduction to Zoology: Chapter 8

The largest, most complex, and most numerous of sponges are the leuconoid sponges. A leuconoid sponge has a thick body wall, and the ostia open into incurrent canals that draw water into the sponge’s body. These incurrent canals open into chambers that are lined with choanocytes. Water flows from these chambers into excurrent canals that empty into a relatively small spongocoel. From there, water exits through an osculum.

Unlike asconoid and syconoid sponges, which are basically built around their spongocoels and oscula, a leuconoid sponge has a complex, irregularly-shaped body that may have several oscula. Its relatively complex body plan allows a leuconoid sponge to have many more choanocytes than can an asconoid or a syconoid sponge, and so it can grow to much larger size.