Polymastia bouryesnaultae, the knobbly sponge, is a small and cryptic species of demosponge from South Africa and Namibia.

They run vertically from the base, expanding into brushes of large spicules whose tips penetrate beyond the cortex.

[1] The cortex is separated from the choanosome by a cavernous boundary that is not entirely free of spicules.

It is made of small, straight tylostyles which are tightly packed with their points directed outwards, projecting beyond the surface of the sponge.

Larger, stout tylostyles are embedded just below this dense layer and project past these points.