awed polychaete annelids are successful in modern oceans, just as they were in early Palaeozoic oceans: the fossil evidence bears witness to abundant and taxonomically diverse faunas. The jaws are composed of sclerotized proteins and were used for grasping in sediment or capturing prey and therefore needed to be resistant to wear. A nuclear microprobe, Particle-Induced X-ray Emission (PIXE) and Scanning Transmission Ion Microscopy (STIM) techniques revealed an enrichment of metals, commonly Zn, Fe and Cu, concentrated mainly at the tips or delicate parts of the jaws. This suggests that accumulation was regulated by the animal and that these elements had functional signficance. Similar enrichment was detected in the jaws of Recent Polychaeta and has also been reported in stress-related, `tool-like' exoskeletal structures of other animal groups, including arthropods, chaetognaths and molluscs