Description:
The exact taxonomic status of this arthropod is in dispute. It has
been termed a “trilobitomorph” by some researchers,
showing their beliefs in its close affinity with the trilobites.
While the Trilobitoorpha was 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 it 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,
with this one, Naraoia spinosa, named for the spinose cuticle so
well preserved here. 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 diverticulae (digestive glands) and the central
gut are evidence, as is the soft cuticle that betrays the outline
of the body. Even if it is not a true trilobite, it is sure to be
a coveted addition to any collection. What makes this one even more
unusual is the fact that some of the internal organs have been preserved
in three dimensions, rather than the typical flat specimens most
often seen.
Also
see: Chengjiang
Biota List Chengjiang
Fossils |