Clathrina mutsu is a species of calcareous sponge from Japan.

The species is named after the type locality, Mutsu Bay[1] The sponge forms irregular, spreading masses consisting of a loose network of ascon-tubes with varying closeness of its meshes in different specimens and in different parts of the same colony.

The oscula are found as small round apertures distributed here and there on the surface of the ascon-tubes.

The diameter of ascon-tubes varies a good deal in different parts of the same colony, measuring about 0.15 - 0.6 mm.

The skeleton is composed of triradiates arranged in a few confused layers in the walls of ascon-tubes.