Hurdia
Hurdia is an extinct genus of hurdiid radiodont that lived 505 million years ago during the Cambrian Period. As a radiodont like "Peytoia" and "Anomalocaris", it is part of the ancestral lineage that led to euarthropods. Description. "Hurdia" was one of the largest organisms in the Cambrian oceans, reaching approximately 20 cm (8 inches) in length. Its head bore a pair of rake-like frontal appendages which shovelled food into its pineapple-ring-like mouth (oral cone). Like other hurdiids, "Hurdia" bore a large frontal carapace protruding from its head composed of three sclerites: a central component known as  the H-element and two lateral components known as P-elements. The function of this organ remains mysterious; it cannot have been protective as there was no underlying soft tissue. Body flaps ran along the sides of the organisms, from which large gills were suspended. Ecology. "Hurdia" was a predator, or possibly a scavenger. Its frontal appendages are flimsier than those of "Anomalocaris", suggesting that it fed on less robust prey. It displayed a cosmopolitan distribution; it has been recovered from the Burgess shale as well as sites in the US, China and Europe. Taxonomic history. "Hurdia" was named  in 1912 by Charles Walcott, with two species, the type species "H. victoria" and a referred species, "H. triangulata". The genus name refers to Mount Hurd. It is possible that Walcott had described a specimen the year prior as "Amiella", but the specimen is too fragmentary to identify with certainty, so "Amiella" is a "nomen dubium". Walcott's original specimens consisted only of H-elements of the frontal carapace, which he interpreted as being the carapace of an unidentified type of crustacean. P-elements of the carapace were described as a separate genus, "Proboscicaris", in 1962. In 1996, then-curator  of the Royal Ontario Museum Desmond H. Collins erected the taxon Radiodonta to encompass "Anomalocaris" and its close relatives, and included both "Hurdia" and "Proboscicaris" in the group. He subsequently recognized that "Proboscicaris" and "Hurdia" were based on different parts of the same animal, and recognized that a specimen previously assigned to "Peytoia" was also a specimen of the species. He presented his ideas in informal articles, and it was not until 2009, after three years of painstaking research, that the complete organism was reconstructed.