Comparative morphology of the dermal denticles of two critically endangered hammerhead shark species (Sphyrna lewini and Sphyrna zygaena - Chondrichthyes, Sphyrnidae)

• Grant number: 24/12844-3
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: May 01, 2025
• End date: April 30, 2026
• Field of knowledge: Biological Sciences - Zoology - Applied Zoology
• Principal Investigator: Otto Bismarck Fazzano Gadig
• Grantee: Núbia Dutra Cunha
• Host Institution: Instituto de Biociências (IB-CLP). Universidade Estadual Paulista (UNESP). Campus Experimental do Litoral Paulista. São Vicente , SP, Brazil

Abstract

Sharks and rays are important to marine ecosystems due to their role as predators. This trophic status is related to their sensory abilities, with several organs dedicated to receiving stimuli of various natures. Among sharks, most of the medium to large species are predators with remarkable sensory capacity, particularlythe smell sense. The hammerhead sharks (Sphyrnidae) have a laterally expanded head, shaped like a "T", at the ends of which are the nostrils and eyes, bringing sensory advantages. Comparative olfactory efficiency between hammerhead shark species has not yet adequately addressed the functional role of dermal denticles in the nasal region conecrning to their efficiency in driving water flow to the nasal openings, bathing the olfactory rosette. In the present study, the morphology of the dermal denticles adjacent to the nostrils of the hammerhead shark, Sphyrna lewini, a large species with worldwide distribution and among the most common in the western South Atlantic, will be analyzed. The material to be analyzed comes from specimens kept in scientific collections or accidental captures. Pieces of skin (~5 mm2) will be removed from each individual from five points in the nasal region, which will be analyzed under a stereoscopic microscope and scanning electron microscopy. The dermal denticles at each point will be measured, described in terms of morphology, orientation and density (per mm2). With the results, we intend to establish a comparison between the different age classes, relating these possible differences to the bio-ecological aspects of the species, such as habitat use and food.