Polymastia hirsuta is a species of sea sponge belonging to the family Polymastiidae.

It is found in various subtidal habitats in the far north of North Island, New Zealand.

This is a usually circular sponge up to 7 cm in diameter.

This rather distinctive species is generally brown and silt-covered but with prominent papillae appearing as bright yellow, silt-free lumps over the whole surface.

This article about a demosponge is a stub.