A function for distinguishing between the long, intermediate and short-setaed forms of Mononychellus species complex is described. The results show that the dorsal-central body setae, variable D3, with a discriminant correlation coefficient of 0.99, was the most important variable. Five other variables, lengths of dorso-central body setae Dl, D2, laterals LI, L2 and propodosomal P2, which had significant discriminant correlations (0.28 to 0.35) with the function were, however, included in the discriminant function.