Fossil reveals an ancient arthropod’s nervous system

Ventral nerve cord controlled critter’s many legs

Chengjiangocaris kunmingensis

ROCK STAR  The ancient arthropod Chengjiangocaris kunmingensis looked crustaceanesque with a large head, long body and paired legs — and a ventral nerve cord (dark horizontal line above the legs is part of a preserved cord). 

Jie Yang

The fossilized remains of an about 520-million-year-old creepy-crawly provides a portrait of an ancient arthropod’s nervous system.

Researchers first described Chengjiangocaris kunmingensis — an ancient relative of spiders, insects and crustaceans unearthed from a fossil bed in southern China — in 2013. Further imaging and investigation of five new fossilized specimens reveal exceptionally well-preserved soft tissue and a ropelike structure running down the animal’s belly. That structure is the remains of a ventral nerve cord, Xi-guang Zhang of Yunnan University in Kunming, China, and colleagues explain February 29 in the Proceedings of the National Academy of Sciences.

In invertebrates, a nerve cord serves the same function as our spinal cord. In C. kunmingensis, bundles of ganglia and connective tissue form the cord just like in today’s tardigrades. Each bundle probably controlled a pair of itty-bitty legs, the researchers write. What appear to be individual peripheral nerves shoot off from the nerve cord, resembling the segmented nerve roots seen in penis worms and velvet worms.

The ancient critter’s nervous system adds to our understanding of the broader evolution of nervous systems in modern invertebrates, the researchers write. 

Helen Thompson is the multimedia editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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