Eldonia eumorpha, Enigmatic Taxon from Chengjiang Maotianshan Shales

Description: This is an enigmatic creature known as Eldonia eumorpha. The species is known from numerous specimens, and is one of the largest animals, sometimes in excess of 100 mm across. Specimens are preserved as a nearly flat impression. Distinct strands radiating from the center are interpreted as radial canals on both the ventral and dorsal surface. The diversity of soft-tissue fossils from the Chengjiang Biotais astonishing: algae, medusiforms, sponges, priapulids, annelid-like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day.

This animal was originally described as a medusoid under the name Stellostomites eumorphus, but subsequently assigned as a species of Eldonia, a genus represented in the somewhat younger Burgess Shale Fauna by Eldonia ludwigi. Some believe there is sufficient difference between them to warrant a new genus for the Chengjiang material. Just as its affinities are enigmatic, so too is its lifestyle. Its medusoid shape is suggestive of a pelagic lifestyle, but other researchers think it led a benthic existence, passively lying on the mud surface. This taxon has only been recorded from the Chengjiang Biota.