EN
Composition and abundance of Gastrotricha in lake psammon were studied and compared with those from other lake habitats. Samples were taken from April till October 2004 from 3 sites at the edge of zone frequently wetted by waves (hygropsammon) in a deep (38 m) mesotrophic lake situated in Łęczyńsko-Włodawskie Lakeland (south-eastern Poland). A total of 11 gastrotrich species belonging to Chaetonotidae family were found. Three species: Lepidodermella squamata Dujardin, Chaetonotus macrochaetus Zelnika i Ch. heideri Brehm dominated (52%) in total abundance. According to the previous studies the number of species occurring in bottom sediments of the same lake was higher by 11–14 species. Species diversity index H’, amounted 2.19 being lower than that calculated for the gastrotrichs of inshore bottom and littoral sediments (2.88 and 2.58, respectively) and similar to the value given for epiphytic fauna (2.01) of that lake. The fauna of psammic Gastrotricha showed the greatest similarity (38%) to epiphytic fauna of that lake as measured by the index of homogeneity. Peak densities of psammic Gastrotricha were found in May (37.5 10³ ind. m⁻²) and in September (32.8 10³ ind. m⁻²) and marked decrease of density was observed in August and October (18.1 10³ ind. m⁻² and 13.6 10³ ind. m⁻², respectively). Mean density and biomass were 25.35 10³ ind. m⁻² and 3.8 mg m⁻² respectively. Density and biomass of Gastrotricha were by two orders of magnitude lower in psammon than in bottom sediments of the lake.