Bloodworms, belonging to the genus Glycera, are marine segmented worms known for their unique adaptation to life in intertidal mudflats. These reddish-pink polychaetes, which can grow quite long, are predators that burrow deep into the sediment. These worms possess a highly unusual jaw structure that incorporates copper. The copper-infused jaws must be tough enough to last the entirety of the worm’s lifespan, which can be up to five years, since they are only formed once.
Bloodworm Jaws and Composition
The bloodworm’s feeding apparatus is not a set of ordinary teeth but a complex, eversible proboscis equipped with four distinct jaw structures. These fang-like jaws, which are only about two millimeters long, are attached to the end of the proboscis and are black in color. They are a sophisticated biocomposite material, consisting primarily of protein, melanin, and copper-based minerals, making them remarkably robust.
Approximately 50% of the jaw’s mass is made up of protein, while melanin accounts for roughly 40%, and copper minerals constitute up to 10% of the total weight. The protein component acts as the structural matrix, while melanin provides strength. The copper is present in two forms: both as a mineral, specifically atacamite, and as ionic copper coordinated within the protein matrix, which functions as a cross-linking agent.
Why Copper? Material Properties
The inclusion of copper provides a distinct mechanical advantage over more common biological hardening agents like calcium carbonate, which is found in shells, or the iron used in limpet teeth. The copper-based mineral, atacamite, is organized into polycrystalline fibers that reinforce the jaw structure, enhancing its hardness and stiffness. This metallic reinforcement allows the jaws to pierce the tough integuments of prey and withstand repeated use without fracturing.
The jaws of Glycera worms exhibit an extraordinary resistance to abrasion, a property that approaches the durability of human tooth enamel. This resistance is necessary because the jaws are subject to constant friction from burrowing through abrasive marine sediments. Furthermore, the ionic copper acts as a structural element, cross-linking the long chains of fibrous proteins to increase the jaw’s overall toughness and resistance to wear.
The Process of Biomineralization
The process by which the bloodworm creates its metallic jaws is a complex feat of biomineralization, starting with the acquisition of copper from its environment. The worm extracts copper ions from the surrounding mud and water. It then uses a specialized molecule, termed a multi-tasking protein (MTP), to manage and incorporate this metal.
The MTP, which is rich in the amino acids glycine and histidine, performs several functions simultaneously to construct the jaw. It first recruits and binds to the copper ions, concentrating the metal into a viscous, protein-rich liquid. This MTP-copper complex then separates from the water, forming a distinct phase that initiates the next step.
The protein uses the bound copper to catalyze the conversion of the amino acid derivative DOPA into melanin, effectively acting as an organizer and a manufacturer. The final step involves the assembly of the protein, copper, and melanin into the rigid films and fibers that form the final, hardened jaw structure.
Feeding Habits and Ecological Role
The highly specialized copper jaws are used in the bloodworm’s predatory feeding strategy. When hunting, the worm rapidly everts its proboscis using hydrostatic pressure, essentially turning its mouth inside out to expose the four black fangs.
The hardened jaws, reinforced with copper, are used to grasp and pierce the victim’s body. The hollow nature of the jaws is significant because it allows the worm to inject venom into its prey, quickly immobilizing it. As a subsurface predator in intertidal zones, the bloodworm plays a role in controlling populations of smaller invertebrates, contributing to the balance of the marine sediment ecosystem.