Mergus is the genus of the typical mergansers, fish-eating ducks in the seaduck subfamily (Merginae). The hooded merganser, often termed Mergus cucullatus, is not of this genus but closely related. The other "aberrant" merganser, the smew (Mergellus albellus), is phylogenetically closer to goldeneyes (Bucephala).Although they are seaducks, most of the mergansers prefer riverine habitats, with only the red-breasted merganser being common at sea.