A new species of Coulmannia, Coulmannia rossensis, is described from the Ross Sea, Antarctica. It is most similar to Coulmannia ramosae Castelló, 2004, but can easily be distinguished from this species bythe males yielding a pair of granulate humps on the dorsum of the pereonites 1-6 and a single granulate hump on the pereonite 7 and the free pleonite. Coulmannia rossensissp. n. is sexually dimorphic. The dorsal sculpture of the female bodies yield a single granulate hump on all the pereonites and free pleonite. The species of the genus Coulmannia are restricted to the Southern Ocean, and Coulmannia rossensissp. n. is the fourth species included in it.
Keywords: Coulmannia; Isopoda; Ross Sea; Southern Ocean; new species; taxonomy.