Rotifers (Rotifera) are microscopic worms from the group Scolecida, which inhabit pelagic and littoral aquatic bioceonoses, including periphyton, psammon, edaphon and various micro-biotopes worldwide. Due to their fast reproduction, rotifers can reach high population densities in fresh and brackish waters, as well as in marine coastal zones, forming an important element in trophic web, especially as starting food for fish larvae. The morphological and functional specificity of trophic structures of rotifers are key element to their contribution to the process of biological self-purification of water bodies. Rotifers play an important role in anthropogenic sediments by acting as bio-filters in waste water treatment plants.

Being rather tolerant to different environmental conditions, many rotifer species are good indicators of water quality and can be used for the ecological monitoring of water bodies. However, the role of certain species in ecosystem functioning is not well known to date. This is largely due to insufficient knowledge on the species composition of bioceonoses. In order to complete this knowledge and inventarize the fauna, information on biogeography along with data on systematics is essential. Ecology of the water body and its geographical latitude location are the main factors that define the distribution of rotifers. A study of the aquatic fauna in the densely populated and polluted NW region of Russia is of exceptional importance.

“Catalogue of the freshwater rotifers (Rotifera) of North-West Russia” includes information on 703 species and varieties belonging to 94 genera and 26 families. Synonyms are given only to species names mentioned in old publications. The inventory includes not only monogonont rotifers, which are more thoroughly studied, but also representatives of the peculiar Bdelloida. This publication includes the first list of bdelloid rotifers from Russian water bodies. The species list presented in this catalogue was compiled on the basis of original and published data on the rotifer fauna of this region, available from the 1830-s through the present. The NW region of Russia is located between Kaliningradskaya Oblast’ in the West and Ural mountains at the East, and from the Russian far North to Moskovskaya Oblast’ in the South. Rotifer studies were carried out in ca. 100 lakes, over 70 rivers, and 10 reservoirs, numerous swamps, wetlands and small water bodies, as well as in terrestrial habitats (mosses and lichens). For each rotifer species the type of water body, geographical location of the collection place, and references are indicated. Most information on the rotifer fauna was taken from publications on zooplankton studies in different water bodies. Therefore, the list of references exceeding 400 citations can be relevant to hydrobiological studies. The authors of this catalogue tried to present as many references as possible, although we can not claim completive.

Analysis and generalization of knowledge on the rotifer fauna of different water bodies in NW Russia can provide valuable information on aquatic fauna, which in turn can be useful for the ecological management in this region. The catalogue can therefore be used as a database for further computer analysis and modeling.

The authors gratefully acknowledge valuable comments and suggestions by S.Ya. Tsalolikhin and thank Vladimir S. Shestakov for preparing the Internet version of the catalogue.