A genus of stomach-infecting parasitic nematodes (family Spiruridae) of birds. When filled with eggs, the female worm is enormously enlarged and has a globular, blood-red appearance. Species include Tetrameres americana, found in the proventriculus of chickens (sometimes severely pathogenic in young chicks), turkeys, grouse, and quail, and transmitted by infected cockroaches and grasshoppers, and Tetrameres fissispina, found in the proventriculum of ducks, geese, wild waterfowl, pigeons, and doves but rarely in gallinaceous birds. [see tetrameric]