Body lengths and widths were measured and body volumes were calculated for 1556 Arctic nematodes sampled from depths of 800-3000 m. The samples were filtered through standard sieves with mesh sizes of 500, 250, 125, 63, and 32 μm. Due to the random orientation of the animal bodies with respect to the sieve plane and the presence of detrital and sediment particles, one can only assess the probabilities of the animal retention over the sieves. The distributions of the logarithms of the body volume and length values of nematodes were close to the normal distribution on the three finer sieves. A simple mathematical filtration model describing size distribution of nematodes on the sieves is proposed. A relation between the mean log lmean value on the sieve and the logarithm of its mesh size log m was obtained: log lmean = a + k log m ; the k values ranged from 0.5 to 1.0 linearly depending on the dispersion of the original size spectra. The limitations for the application of this relation are discussed.