Osteological insights on Turkish <i>Pseudophoxinus</i> species and <i>Egirdira nigra</i> (Teleostei: Leuciscidae)

Abstract The present study aims to provide a comprehensive comparative analysis of the vertebral column, fin structure and caudal skeleton of 21 species of Pseudophoxinus and Egirdira nigra (Family: Leuciscidae) collected from various freshwater locations across Türkiye. Using mammographic imaging, eight distinct characteristics of the vertebral column and caudal skeleton were examined: the structure of the vertebral column, vertebral column regionalization, interdigitation of the pterygiophores with the neural spines of the dorsal fin, interdigitation of the pterygiophores with the haemal spines of the anal fin, the caudal fin formula, distribution of the dorsal procurrent caudal fin, distribution of the ventral procurrent caudal fin and the description of the caudal fin skeleton. These features were documented for all species studied. The findings reveal that osteological data vary among the species examined, highlighting that the structure of the vertebral column and caudal skeleton can serve as valuable tools in the taxonomic classification of Pseudophoxinus species and E. nigra . Additionally, this study introduces a novel approach for defining the regions of the vertebral column, dividing it into four distinct regions: postcranial, middle (comprising both anterior and posterior sections) and caudal regions. Furthermore, the research identifies specific osteological features that could serve as effective taxonomic criteria to differentiate E. nigra from the species within Pseudophoxinus . This new anatomical data contributes to a deeper understanding of the taxonomy and systematics of these species in Türkiye.