Variation in taxonomic characters from Tetrastemma laminariae (Hoplonemertini, Nemertini) was analysed by, and expressed in, different types of statistics (coefficient of variation, range, coefficient of residual variation and variance of logarithms). Variance based on log-transformed values makes it possible to test differences in variation between populations. The variation was high in most characters, probably owing to artifacts, especially contraction on fixation. Because of this the species have to be diagnosed by many characters, properly stated not only by their mean values but also by their variation. The number of accessory stylets in a starved population was tested and found significantly (P=005) higher than in a freshly sampled population. There was no difference between these two populations in the length of the main stylet.