Regional Microarchitecture of the Skin of the Arabian Carpetshark (Chiloscyllium arabicum): A Histological Study Using Polarised Light Microscopy.

The integument of elasmobranchs is a complex biomechanical system in which epithelial, connective tissue and mineralised components form a functionally specialised body surface. Despite extensive research on dermal denticles, the spatial configuration of the whole integument, especially the regional arrangement of collagen fibres in benthic species, remains poorly understood. This study provides an integrated characterisation of the skin microarchitecture of the Arabian carpetshark (Chiloscyllium arabicum), with emphasis on regional variability in dermal denticles and collagen matrix structuring. Skin samples were analysed using haematoxylin and eosin, Masson-Goldner, PAS-Alcian blue and picrosirius red staining, together with transmitted and polarised light microscopy and morphometric analysis. The skin of this species showed a hierarchical organisation comprising a stratified epithelium and a complex fibrous dermis. Dermal denticles displayed typical elasmobranch anatomy, but their morphology, orientation, and density varied regionally, allowing five morphotypes to be distinguished. Collagen fibres formed ordered, plywood-like and orthogonal arrangements showing spatial correspondence with local denticle distribution. These findings indicate regional structural specialisation of the integument and suggest a structural association, and a possible functional relationship, between denticle morphology and collagen architecture.