  the seaducks (merginae) form a subfamily of the duck, goose and swan family of birds, anatidae. as the name implies, most but not all, are essentially marine outside the breeding season. many species have developed specialized salt glands to allow them to tolerate salt water, but these are absent from juveniles. some of the mergansers prefer riverine habitats. all but two of the 20 species in this group occupy habitats in far northern latitudes. the fish-eating members of this group, such as the mergansers and smew, have serrated edges to their bills to help them grip their prey. these are therefore often known as "sawbills". other seaducks take molluscs or crustaceans from the sea floor. ==species== there are twenty living species in ten extant genera. subfamily merginae *genus â chendytes, the diving-geese. these birds became extinct in prehistoric times. they were large, goose-like ducks with reduced wings which were unfit for flying, but could assist in diving as in the great auk. at least one species survived to the holocene. ** â chendytes lawi *genus polysticta **steller's eider polysticta stelleri *genus somateria, the eiders. these are large marine ducks. the drakes have body plumage showing varying amounts of black and white, and distinctive head patterns. females are brown. ** common eider somateria mollissima ** spectacled eider somateria fischeri ** king eider somateria spectabilis *genus histrionicus ** harlequin duck histrionicus histrionicus *genus â camptorhynchus ** â labrador duck camptorhynchus labradorius (extinct) *genus melanitta, the scoters. these are stocky marine ducks. the drakes are mostly black and have swollen bills. females are brown. ** common scoter melanitta nigra ** black scoter or american scoter melanitta americana (sometimes considered a subspecies of m. nigra) ** velvet scoter melanitta fusca ** white-winged scoter melanitta deglandi (sometimes considered a subspecies of m. fusca) ** surf scoter melanitta perspicillata *genus clangula ** long-tailed duck or oldsquaw clangula hyemalis *genus bucephala, the golde
Bird_subfamilies Mergansers Merginae