Vodní měkkýši dolního toku Chrudimky – jediná lokalita Unio crassus v Pardubickém kraji? [Aquatic molluscs of the lower stretch of the Chrudimka River – the only site of Unio crassus in Pardubice Region?]

This paper presents results of a malacological survey of the Chrudimka River between the town of Chrudim and the junction with the Labe (Elbe) River; the territory of the Dolní Chrudimka Site of Community Importance (SCI). Twenty-three species of aquatic molluscs (11 gastropods and 12 bivalves) were found at 21 sites during the research in 2013, 2015 and 2016. The occurrence of a population of rare bivalve Pseudanodonta complanata was recorded in the lower stretch. The research was focused on the population of the endangered bivalve Unio crassus which occurrence was confirmed at nine sites, however its population density was always low. The Chrudimka site is nowadays the only site with the occurrence of this bivalve known in Pardubice Region (Czech Republic, Eastern Bohemia).