Abstract: A ciliate to be very image of Stylonychia mytilus in body shape and cortical morphology was found in marsh water of Morshan Town in Heilongjiang Province.Only the macronucleus of the present species is nodulated,this feature is contrary to the traditional diagnosis of the genus Stylonychia.However,the feature that the replication bands are two and appear at both ends in S phase of the macronucleus is still similar to that of Stylonychia.Moreover,in view of the fact that different shaped macronucleus may exist in the same genus of other hypotrichs (Borror,1983),the authors determined to set down it as a new species in the genus Stylonychia rather than establish new genus for it,and name it Stylonychia nodulinucleata sp.nov.Thus the traditional diagnosis on the macronuclear shape of the genus must be revised.