Primicaris
larvaformis
Phylum Arthropoda
Geological
Time: Early Cambrian (~525 million years ago)
Size: 4
mm long by 2.5 mm wide
Fossil
Site: Chengjiang Maotianshan Shales, - Quiongzhusi Section, Yu’anshan
Member, Heilinpu Formation, Ercaicun Village, Anning, Kunming, Yunnan,
China
Description:
The exact taxonomic status of this arthropod is in dispute. It has
been termed a “larval 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. It was once thought to be a larval form of Naraoia. The Naraoiidae
are arachnomorphs and include Misszhouia and Naraoia,. Studies of
additional specimens in 1997 led to the establishment of a new genus
Primicaris, with the genus name larvaformis drawing attention to
its larval appearance. It is quite well preserved, certainly as
good as the 70 specimens that were recovered over a decade ago.
With a size range known of 2-6 mm, this one is right in the center
of that range. The primitive aspects of body plan suggest it may
be a basal arachnomorph with affinities to the Vendian arthropod-like
animal Parvancorina. The most distinctive feature of this specimen
is that it is preserved in dorsal fashion with the limbs clearly
evident through the cuticle and around the border of the body.
Also
see: Chengjiang
Biota Fauna List Chengjiang
Fossils
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