Morphology of dermal denticles of the Galapagos bullhead shark Heterodontus quoyi (Elasmobranchii: Heterodontidae), a Southeast Pacific shark

Abstract

Dermal denticles, also known as placoid scales, are structures that cover the body of sharks, which functions are diverse and include protection, defense, bioluminescence, and hydrodynamics, among others. These structures have a great variety of shapes and sizes, used in functional and taxonomic studies in chondrichthyans. Despite this, few studies have reported descriptions of dermal denticles from different regions of the body. The objective of the present study was to describe the morphology of dermal denticles of the Galapagos bullhead shark Heterodontus quoyi, examining dermal samples from the dorsal, ventral and lateral areas of the body, in addition to the first dorsal fin. To achieve this objective, four adult specimens were collected from the Fishing Terminal of Santa Rosa, Lambayeque, Peru. The denticles were photographed, measured (length and width), quantified (density) and morphologically described. The results showed differences among the four regions in terms of: (1) density, (2) shape of the crown, (3) size of the crown and (4) shape and number of ridges and cusps on the crown. These observed variations could be useful for future taxonomy studies in identification of the species and ecology as the relationship between its function and region of the body.