Those that are not called weasel include the stoat , the two species of mink , and the polecats or ferrets . Of the 17 extant species currently classified in the genus Mustela , ten have `` weasel '' in their common name . Among those that do not are the stoat or ermine , the polecats , the ferret , and the European Mink ( the superficially similar American Mink is now regarded as belonging in another genus , Neovison ) .