Tooth morphology of deep-water catsharks of the genus Apristurus (Chondrichthyes: Pentanchidae) in the North Atlantic Ocean.

The deep-water catshark family (Pentanchidae) is the most species-rich family among extant shark lineages. Within this family, the genus Apristurus is the largest, comprising small, deep-sea species characterised by elongated bodies and dorso-ventrally compressed snouts. Five Apristurus species are currently recognised from the North Atlantic, including waters surrounding Ireland and the United Kingdom (A. aphyodes, A. laurussonii, A. manis, A. melanoasper and A. microps). However, their biology remains poorly understood owing to their occurrence at considerable depths and their close morphological similarity. This study presents the first comprehensive comparative analysis of tooth morphology for Apristurus species recorded in the region. The results reveal pronounced sexual dimorphism in A. aphyodes and provide evidence supporting ontogenetic changes in tooth morphology in A. melanoasper and A. microps. Furthermore, distinctive morphological characteristics are identified and described for each species using scanning electron microscopy of the dentition. These findings establish novel diagnostic criteria that enhance the reliability of species identification and provide a robust framework for future taxonomic and ecological research.