Atagema osseosa is a species of sea slug or dorid nudibranch, a marine gastropod mollusk in the family Discodorididae.

[2][4] This species is found in the tropical Indo-West Pacific Ocean,[3][4] with records at least from the coasts of India and eastern Australia.

[4] This nudibranch has evolved to mimic closely in appearance the sandy-coloured sponge on which it both lives and feeds off.

[3] Like many nudibranchs, this species feeds on sponges.

This Discodorididae-related article is a stub.