Biomineralization of Mantis Shrimp Dactyl Club during Development: Apatite Formation and Brominated Organic Components

The stomatopod Odontodactylus scyllarus uses weaponized clubs like appendages to attack its prey. These clubs are made of apatite, chitin, amorphous calcium carbonate, and amorphous calcium phosphate ordered in a highly hierarchical structure with multiple regions and layers. We follow the development of the biomineralized club as a function of time since formation using clubs harvested at specific times since molting. The clubs are investigated using a battery of techniques to unravel the biomineralization history of the clubs. Nano focus synchrotron x-ray diffraction and x-ray fluorescence experiments reveal that the club structure is more controlled having more regions than previously thought. The recently discovered impact surface has crystallites in a different size and orientation compared to those in the impact region. The crystal unit cell parameters vary to a large degree throughout individual samples, indicating a large degree of chemical substitution variation, EDS and Raman spectroscopy show that this variation cannot be explained by carbonation and fluoridation of the lattice alone. X-ray fluorescence and mass spectroscopy show that the impact surface is coated with a thin membrane rich in bromine that forms at very initial stages of club development. Proteomic studies show that a fraction of the club mineralization protein-1 has brominated tyrosine suggesting that bromination of club proteins at the club surface is an integral component of club design. Taken together, the data unravel the spatio-temporal changes in biomineral structure during club formation.