Osteological characters of the axial skeleton and pectoral girdles in some species of the Euroasian freshwater fishes of the family Cottidae

Abstract

The structure of the pectoral fin, its girdle and osteological details of the axial skeleton and a skeleton of the caudal fin, including the structure of unpaired fins were studied in three species of three genera of the family Cottidae: the genus Cottus: European species C. koshewnikowi Gratzianov, 1907 and two species of Fareastern monotypic genera: Trachidermus fasciatus Heckel, 1837 and Mesocottus haitej (Dybowsky, 1869). The species well differ in structure of the pectoral girdles and pleural ribs. Mesocottus haitej is characterized by absence of the interradial and coracoid fenestrae and by considerable reduction of pleural ribs in the abdomen part of the vertebral column. Сottus koshewnikowi and T. fasciatus have backwardly directed pleural ribs (3 pairs of ribs in M. haitej). Trachidermus fasciatus is characterized with the most number of plesiomorphic features: the presence of branched rays in the pectoral fin, greater numbers of vertebrae, rays in the second dorsal, anal and pectoral fins, big anteanal distance and by number of preural vertebrae, supporting the procurrent rays. In C. koshewnikowi, the first dorsal fin occupies the most anterior position: aID 32.6–38.0% SL vs 35.7–38.7% SL in T. fasciatus and 36.4–40.8% SL in M. haitej.