A total of 175 morphospecies belonging to 47 genera of the monogonont Rotiferaare reported here, representing the highest rotifer biodiversity recorded from any body of water in Turkey; 34 of these species are new records for the Turkish fauna. The genera Donneria De Smet, Octotrocha Thorpe and StephanocerosEhrenberg are recorded for the first time in Turkey. The eastern Oriental taxonBrachionus murphyi Sudzuki and the tropicopolitan Trichocerca braziliensis(Murray) are new records for both the Palearctic region and western Asia. Additionally, the Palearctic European species Cephalodella cf. ungulata Fischer and Ahlrichs and Lecane margalefi De Manuel are recorded for the first time in Asia and for the second time outside of their type localities. The Tigris River is the third locality reported for the distribution of Donneria sudzukii (Donner). All observed species were members of 23 families with the majority (72%) of the examined fauna belonging to the following families: Notommatidae (33 species) >Lecanidae (30 species) > Brachionidae (25 species) > Dicranophoridae (14 species) > Lepadellidae (13 species) > Trichocercidae (11 species). Littoral rotifers made a significant contribution to the overall species diversity observed. Due to the strategic geographic position of Turkey, it is important to conductspecies inventories in different localities of the country to fill distributional gaps for many rotifer species. The rotiferan species richness found in the study region and the biogeographically interesting elements of this river are remarkable and are discussed here. Additionally, this report represents the most up-to-date review of Turkish rotifers.

Key words: Turkey, Tigris River, species composition, biodiversity, biogeography.