Description: The Bear Gulch Limestone is a deposit of some 70 square km in extent and 30 m in depth that has been a source of one of the most diverse assemblages of fossil fish with some 110 species having been described over the past 30 years. Most were new to science, and provided a unique view of the marine environment of Mississippian times. Fine preservation of both fish and invertebrates is a hallmark of these deposits, presumably due to an anoxic depositional environment. This specimen is a rarely seen member of the Polychaetae, or Bristleworms. The polychaete worms are related to earthworms and leeches, well-known members of the Phylum Annelida. They derive their common name from the setae (or chaetae – bristles) on each side of the body which can be seen here in the central part of the body. The Polychaetae can trace their fossil record back to the 520 million year old Burgess Shale where examples such as Burgessochaeta and Canadia have been preserved.