2. Babka gymnotrachelus (Kessler, 1857), Racer Goby

Gobius gymnotrachelus Kessler, 1857: 464; type locality: Dniester River and its tributaries, especially River Slutsch; syntypes: ZIN 2105 (1, lost).

Etymology: Greek, gymnus = naked + Greek, trachelos = neck, refers to the limited predorsal squamation.

Distribution and habitat: Black Sea, Sea of Azov, and Caspian Sea basins (Fig. 8A). The species was originally recorded from the Middle and South Caspian Sea, but in recent times has not been recorded farther south than Divichi (Azerbaijan) in the Middle Caspian Sea on the western coast and Kuuli (Turkmenistan) on the border between the Middle and South Caspian Sea on the eastern coast (Ragimov 1965, 1967; Pinchuk et al. 2003e). Due to historical data from the South Caspian Sea, the species was included in the list. Therefore, its present presence in the South Caspian Sea and Iranian waters needs confirmation. In the Caspian Sea basin, it inhabits oligohaline waters of low salinity, sometimes also found in mesohaline environments, but reportedly does not penetrate into rivers and other freshwaters (Pinchuk et al. 2003e). In contrast, in the Black Sea region, B. gymnotrachelus inhabits fresh waters and moderate salinity habitats, for which a molecular genetic analysis of the Black Sea populations was undertaken by Ohayen & Stepien (2007) using mtDNA cytochrome b sequences, which can provide a valuable comparison for the Caspian Sea population group.

Remarks: Berg (1949) considered the Caspian Sea population as a distinct subspecies, Neogobius gymnotrachelus macrophthalmus (Kessler, 1877), on the basis of several morphological features. Pinchuk (1977) noted additional morphological differences. Fricke et al. (2022) based on Esmaeili et al. (2010) recognized the Caspian Sea population as Babka macrophthalma (Kessler 1877), but apparently, those studies were not based on examination of specimens. Therefore, a detailed morphological and molecular analysis of individuals comparing the two basins is needed.

IUCN: LC (Freyhof & Kottelat 2008a).