A physical model simulating contraction of the m. erector tenaculi in Callorhinchus capensis

The frontal clasper is an unpaired courtship structure that develops in male chimaeras during sexual maturation. Although it is known to be mobile, the biomechanics of this movement and the responsible musculature remain poorly understood, particularly in plow-nosed and long-nosed chimaeras. This study addresses these gaps using MRI-based three-dimensional reconstructions and dissections of the tenacular region in two species of plow-nosed chimaeras and one species of long-nosed chimaera. In all specimens, a distinct muscle bundle originating from the jaw adductor was identified and is here named m. erector tenaculi. Its fibres originate beneath the base of the tenaculum near its posterior margin and insert onto a connective tissue “sole” under the skin ventral to the tenaculum. Physical modelling showed that contraction-induced bulging of this muscle elevates the tenaculum.