Species of sponge from southern Africa
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Polymastia bouryesnaultae, the knobbly sponge, is a small and cryptic species of demosponge from South Africa and Namibia. 
Description.
Although the holotype of this species was collected in 1999, it was not described until 2005. 
It has a thickly encrusting to semi-spherical form and is firm and tough. It grows up to long and wide. The fuzzy brown surface has numerous pale yellow to light brown smooth, tapering projections (papillae). The papillae are various sizes, growing up to high and wide. The oscules are not visible. 
Spicules.
This sponge only has megascleres, no microscleres. The following megascleres are present:
Skeleton.
The choanosomal skeleton is made of well-formed tracts of megascleres. They run vertically from the base, expanding into brushes of large spicules whose tips penetrate beyond the cortex. Ectosomal and intermediate size spicules occur randomly in the choanosome.
The cortex is separated from the choanosome by a cavernous boundary that is not entirely free of spicules. The cortex is very dense. 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.
Distribution and habitat.
This species is known from the south and west coasts of South Africa and the coast of Namibia. It is found on rocky boulders at depths of . It is usually found in association with other sponges.