A relict and endemic species of the Blue Nile drainage basin, the mussel Unio abyssinicus, is under the threat of extinction, with the continuing decline in the area, while data on the localities and biology of the mollusc are scarce. A new find of the mollusc population in the Duko river, located in the Oromiya Region of south-western Ethiopia, gives additional information about distribution of this species. The morphology of siphons of U. abyssinicus has been studied for the first time, the features of siphonal papillas are compared with those of the other mussel species. The data on the beak sculpture as well as the morphology of the hinge teeth have been clarified. Some new data on biology of the mussel are provided.