Allozymic, karyological and morphological analyzes confirmed the presence of the Thick-clawed crayfish, Astacus pachypus (Rathke, 1837), in Ukraine. Th is rare species in Ukraine is found only in two small adjacent localities restricted to the Lower Dnieper. It is characterized by a unique set of chromosomes (2n = 116) and a distinct pool of allozymes, allowing, together with morphological features, to clearly distinguish it from the other three species of the Ukrainian fauna.
The existence on the territory of Ukraine of two sympatric widespread species definitely different by their chromosome number was proved based on the meiotic chromosome preparations. Besides the nominal species Pontastacus leptodactylus (Dana, 1852) with modal haploid chromosome number n = 93 we prove the existence of P. angulosus (Rathke, 1837) with n = 88.