Gobius nonultimus Iljin, 1936: 337 Gobies (Teleostei: Gobiidae) of the oldest and deepest Caspian Sea sub-basin: an evidence-based annotated checklist and a key for species identification Zarei, Fatah Esmaeili, Hamid Reza Abbasi, Keyvan Kovačić, Marcelo Schliewen, Ulrich K. Stepien, Carol A. Zootaxa 2022 2022-09-28 5190 2 151 193 423LC (Iljin, 1936) Iljin 1936 [193,618,1051,1078] Actinopterygii Gobiidae Mesogobius Animalia Perciformes 22 173 Chordata species nonultimus      Gobius nonultimus Iljin, 1936: 337, fig. p. 325; type locality: 24 milessouthwest of Ulsky Bank, Caspian Sea, depth 24 mabove a bottom depth of 54 m, Turkmenistan; types: the holotypeof this species, an adult female of 107.5 + 19.5 mmappears to be lost.   Etymology: Iljin (1936)did not provide an explanation of the specific name.   Distribution and habitat:Widely distributed in the open sea in all three areas of the Caspian Sea.A relatively deepwater mesohaline species ( Pinchuk & Miller 2004d).   Remarks: Kessler (1877)described  Gobius nigronotatusfrom a single specimen, taken on the border between the North and Middle Caspian Sea areas at Fort Aleksandrovskiy, near Mangyshlak ( Kazakhstan) at 43 m, and the brief definition of this species provided by Berg (1949)corresponded in a number of characters with  M. nonultimus(Iljin), but differed chiefly in the alleged absence of head scales in the former and in the presence of six rather than seven first dorsal rays. However, D.B. Ragimov found just six first dorsal rays in material identified as  M. nonultimusand small head scales that may be easily overlooked, as likely was the case before contemporary binocular microscopes and staining techniques. Pinchuk & Miller (2004d)tentatively synonymized those two nominal species. However, in the case that both species truly are conspecific, then  M. nigronotatus( Kessler, 1877)would become the senior synonym for the taxon. A detailed morphological and molecular analysis of samples from the three Caspian Sea areas is warranted.   Material examined:  ZM-CBSUS036, 1, off Anzali, Gilan Province, Iran.  IUCN:DD ( Larson 2019b). 3914046326 [394,983,223,249] ZM-CBSU Iran -36.1 Anzali 23 174 1 Gilan