The relationships between epiphytic fauna and habitat conditions were studied in three oxbow lakes of Wieprz River (eastern Poland). Fauna associated with macrophytes showed low species richness (range 8–11 taxa dependently on site and season) usually observed in lakes of high water trophy. Densities of fauna were high (mean 71–5250 ind. 100 g DW-1), typical for shallow lakes with well developed submerged vegetation. In the domination structure prevailed Gastropoda (relative abundance 23–100%) and Chironomidae (relative abundance 8–87%). Re-dundancy analysis showed the significance of four environmental variables – temperature, dis-solved oxygen, Ptot and P-PO4 as determinants of abundance of epiphytic fauna.

The research was carried out on species diversity, density and similarity of Gastrotricha living on two species of macrophytes Myriophyllum spicatum L. and Elodea canadensis Michx. in a mesotrophic lake. Gastrotricha occurring on the studied macrophytes were represented by 23 species (21 on M. spicatum L. and 22 on E. canadensis Michx.). Species diversity (expressed by the Shannon index) for the Gastrotricha occurring on the two studied species of macrophytes amounted to 2.70 for M. spicatum L. and 2.81 for E. canadensis Michx., what suggests equal distribution of the gastrotrich species revealed in the studied species of macrophytes. The definite dominants inhabiting the two species of macrophytes were: Heterolepidoderma macrops Kisielewski, 1981, Heterolepidoderma ocellatum (Mečnikow, 1865), Lepidoderma squamata (Dujardin, 1841) and Aspidiophorus squamulosus Roszczak, 1936, and their inclusive percentage participation in the whole gastrotrich fauna for M. spicatum L. and E. canadensis Michx. was 41.8 and 40.3% respectively. The domination structure of the gastrotrich fauna of the two species of macrophytes was similar for each gastrotrich species (G-test, for all p > 0.05). Average density of Gastrotricha inhabiting M. spicatum L. amounted to 588.0 10³ indiv. m-2, and density of Gastrotricha occurring on E. canadensis Michx. amounted to 670.0 10³ indiv. m-2. Statistic analysis based on the Mann-Whitney test showed that differences of the gastrotrich densi-ty on the studied species of macrophytes: M. spicatum L. and E. canadensis Michx. (Z = -1.9282; p = 0.05) are statistically insignificant.

The species diversity, density and similarity of Gastrotrich fauna of bottom sediments to epiphytic fauna in three farm ponds were investigated. In the studied habitats 31 species of Gas-trotricha belonging to the family of Chaetonotidae were found altogether. In bottom sediments of the ponds there were 29 and on plants 17 species of Gastrotricha. Three species (Heterolepido-derma gracile Rmane, 1927, Chaetonotus disjunctus Greuter, 1917 and Ch. oculifer Kisielewski, 1981) were found to be dominants in bottom sediments with the dominance over 10.0%. H. gracile and Ch. oculifer also occur on vegetation, but their dominance is significantly lower. In turn three species (H. macrops Kisielewski, 1981, H. ocellatum (Mečnikow, 1865) and Lepidodermella squamata (Dujardin, 1841) proved to be dominant on water vegetation, with the dominance over 10.0% in all studied ponds. The value of species diversity index H’ including the number of spe-cies and uniformity of their dominance is from 2.76 to 2.93 for bottom sediments and from 2.60 to 2.72 for plants. The total density of gastrotrich fauna in bottom sediments fluctuated from 350.0 to 920.0 103 indiv. m-2 and on elodeids from 520 to 1110 103 indiv. m-2. The density of gastrotrich fauna of elodeids was higher than in bottom sediments in all the studied ponds. In each of the ponds examined, the differences are statistically significant. The similarity between bottom sediment fauna and epiphytic fauna in each of the studied ponds, cal-culated according to the homogeneity index, was very low and ranged from 44% to 48%.