Marine polychaete worm jaws are biting structures that are designed and adapted, like vertebrate teeth, for impact and wear. Nereis jaws are a remarkable natural material to study for its superior mechanical properties. Most importantly, Nereis jaws contain no detectable mineral components but their hardness and stiffness is comparable to that of dentin which contain ∼ 70% mineral. Further, to resist contact damage, Nereis has evolved mechanical gradients that correlate with molecular gradients in the jaw. Little is known of the chemical and structural components that play a role in the jaws mechanical properties. In this dissertation, some breakthroughs in the chemistry of Nereis virens jaws are presented. Using Secondary Ion Mass Spectrometry (SIMS), X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM) the relationship between ultrastructure, halogen (Cl, Br and I), metal (Zn, Na, Si, Al, Fe, K, Mg and Ca) gradient distributions, and chemical nature was explored. The outer surface coating of the jaw-tip appeared to have a granular morphology (∼ 3 to 8 pm thick), in contrast to the anisotropic, fibrous core that dominates the sub-architecture. Given the narrow distributions of some metals in the granular jaw coating, it is possible that they contribute to mechanical properties such as wear. Furthermore, using analytical techniques such as chromatography and mass spectrometry we have found that the halogens are associated with proteins in the jaw. Halogenated histidine, tyrosine, dityrosine and trityrosine amino acids have been characterized. Several modified amino acids have been discovered here for the first time: di-bromo-histidine, bromo-iodo-histidinc, chloro-iodo-tyrosine, bromo-iodo-tyrosine, chloro-di-tyrosine, chloro-tri-tyrosine, chloro-bromo-tri-tyrosine and bromo-iodo-tri-tyrosine. Inspired from the new knowledge obtained thus far, the role of bromination in Nereis jaws was explored with an imidazole model system. The function of halogenation in the jaws is not known, however, it is hypothesized that they stabilize the proteins, protect it from chemical or microbial attack and indirectly contribute to the mechanical properties of this natural biological material.