The crayfishes (Decapoda: Astacidea: Astacidae) of Azerbaijan: taxonomic challenges and distributional insights

Abstract

Azerbaijan hosts a historically contentious crayfish fauna shaped by the complex biogeography of the Ponto-Caspian region and a legacy of Soviet-era taxonomy. Crayfish species richness in the region has varied from one to six species, largely due to unresolved synonymies of Pontastacus Bott, 1950, the mixing of freshwater and Caspian brackish-water taxa, and persistent misinterpretations of early literature. The review provides the first comprehensive, country-level synthesis of the crayfish species of Azerbaijan evaluated within a modern systematic and biogeographic framework. By reassessing historical records, taxonomic revisions, and regional distribution data, we clarify the composition and status of crayfish taxa attributed to the fauna. The available evidence demonstrates that only two species, Pontastacus leptodactylus (Eschscholtz, 1823) and the endemic P. pylzowi (Skorikov, 1907), are reliably established in freshwater environments. Pontastacus eichwaldi (Bott, 1950) is known in the Lankaran sector of the Caspian basin but remains unverified, while the Caspian brackish-water P. pachypus (Rathke, 1837) and P. kessleri (Schimkewitsch, 1886) cannot be considered freshwater components of the fauna. The frequently cited Astacus astacus Kessler, 1876 is shown to represent a taxonomic artifact rather than a valid element. Documented population declines in the two confirmed freshwater species underscore the need for renewed field surveys, molecular barcoding to resolve species boundaries, and targeted conservation measures.