Background. Five species of Ponticola have hitherto been recognized among freshwater gobies in the Ponto–Caspian basin. In 2014 a number of specimens representing this genus were collected in northern Iran. The detailed morphological and karyological study of those gobies collected revealed significant differences between them and their known congeners. The aim of this study was to describe these fish as a new species from the Caspian Sea basin. Materials and methods. The fish specimens were collected in August 2014 at two localities of the Sefid-Rud River drainage, and in the Gisum River, Guilan Province, northern Iran. In total, 18 specimens were used for karyological study following a previously described method. Both karyotyped and intact specimens were then morphologically investigated using characters developed for study on gobiids, and particular for freshwater Caucasian gobies. The comparative materials were specimens from museum collections, as well as published descriptions, illustrations, and measurements of other species. Results. Ponticola iranicus sp. nov. differs from its congeners in a set of the following features: D1 VI, D2 I/(14½) 15½ – 17½, A I/10½ – 13½; nape scaled completely, scales cycloid; cycloid scales covering upper part of opercle; lateral line system with posterior sub-orbital row d2 continuous; predorsal area uniform, dark grey; first dorsal fin with oblique black stripe between first two or three rays; short dark grey strip on upper part of pectoral fin base; karyotype consisting of 46 acrocentric chromosomes. Conclusion. All known  Ponto–Caspian gobies demonstrate mosaic pattern of morphological and karyological features that presumes their polyphyletic origins. Further phylogenetic studies by molecular genetic methods are necessary for identification of their marine ancestors and clarifying of common trends in the evolution of the Ponto–Caspian goby group.

Ponticola iranicus sp. nov., description of a new species, freshwater gobies, taxonomy, Ponto–Caspian basin, Iran