Kalmar "Genus Mergus" tana nufin ƙungiyar agwagi masu nutsewa waɗanda ke cikin dangin Anatidae. Wannan rukunin ya ƙunshi nau'ikan agwagwa da dama waɗanda aka san su da iya nutsewa a ƙarƙashin ruwa don neman abinci. Kalmar “genus” tana nufin rarrabuwa taxonomic da aka yi amfani da ita a cikin ilmin halitta zuwa jinsin rukuni waɗanda ke da halaye na gama gari da zuriya. Mergus shine sunan jinsi, wanda ake amfani da shi don nufin duk nau'in agwagwa masu nutsewa da ke cikin wannan rukuni.