Juvenile Naraoia spinosa, Spinose Arthropod from Chengjiang
Often described as a soft bodied trilobite

Name: Naraoiidae; Naraoia spinosa

Geological Time: Early Cambrian Qiongzhusi Section, Yu'anshan Member, Heilinpu Formation (~525 million years ago)

Size: 5 mm

Fossil Site: Chengjiang Maotianshan Shale, Qiongzhusi Section, Yu'anshan Member, Heilinpu Formation, Mafang Village, Haikou County, Kunming, Yunnan Province, China

Naraoia spinosaThe exact taxonomic status of the arthropod Naraoia is in dispute. It has been termed a “trilobitomorpha” by some researchers, indicating their beliefs in its close affinity with the trilobites. While the Trilobitoorpha is listed in the Treatise, most now consider that this subphylum is invalid, a catchall much like some of the dustbin terms used by Walcott for a number of the Burgess Shale fauna. Whittington termed Naraioa a “soft-bodied trilobite”’ but that belief is not supported at present. Their similarity in appearance to the Agnoistida is purely a result of convergence. Two large groupings of the Paleozoic arthropods are currently in favor: the Crustaceomorpha (which includes Waptia) and the Arachnomorpha, dominated by the trilobites. The Naraoiidae are arachnomorphs and include Misszhouia and Naraoia. The species is one found in several locations within Yunnan Province. The diversity of soft-tissue fossils is 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 one shows many of the classic features of the taxon. Even the central gut is in evidence, as is the soft cuticle that betrays the outline of the body. Naraoia spinosa is only known from the Chengjiang Biota. This is a most unusual juvenile example (I have included a photo of an adult for scale) with exceptional soft tissue preservation for which Chengjiang is famous.

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