Mergus is the genus of the typical mergansers, fish-eating ducks in the seaduck subfamily (Merginae). The genus name is a Latin word used by Pliny and other Roman authors to refer to an unspecified waterbird. 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).