Vanadium in the radular teeth of the Antarctic Aegires albus (Nudibranchia)

Radular teeth are increasingly recognized as functionally graded composite structures, yet such structure-property relationships remain poorly understood, especially in species from remote habitats. Here, we investigated the radular teeth of the Antarctic sponge-feeding nudibranch Aegires albus using scanning electron microscopy, confocal laser scanning microscopy, energy-dispersive x-ray spectroscopy, and nanoindentation. We compared the elemental composition of tissues, tooth coating, and inner tooth structure and analyzed regional mechanical gradients within the coating. Both the tooth coating and the inner structure contained calcium and vanadium, whereas these elements were much less abundant in the nonradular tissues. Within the coating, both elements showed clear regional gradients. The coating also exhibited pronounced mechanical gradients: Young's modulus and hardness were lowest in the basis and plate, intermediate in the inner structure, and highest in the stylus and tip. Both calcium and vanadium were positively associated with the mechanical properties in all regions of the teeth. These results show that the radular teeth of A. albus are spatially differentiated, multimaterial structures likely adapted to repeated interaction with spicule-bearing sponge prey. In addition, this study documents substantial amounts of vanadium in radular teeth for the first time.