A new study in Nature Communications describes the exceptionally preserved nervous system of the soft-bodied euarthropod Mollisonia symmetrica from the mid-Cambrian Burgess Shale in British Columbia.
Mollisonia symmetrica is a member of a relatively inconspicuous group of euarthropods knows as mollisoniids, which have a simple dorsal exoskeleton consisting of a head shield, multisegmented trunk, and a posterior shield. Although recent studies suggest that mollisoniids are related to chelicerates, whose extant representatives include horseshoe crabs and arachnids, little was known about their internal anatomy.
The study led by Professor Javier Ortega-Hernández and members of his lab, examined specimens with exceptionally preserved internal organs, such as the digestive system and neurological remains including the optic nerves, the ganglionated ventral nerve cord, and even branching segmental nerves.
"Altogether, the results suggest that Mollisonia's central nervous system is an ancestral relative to that of extant chelicerates," Ortega-Hernández said, "which can help us understand the early history of the group, but also suggest a complex pattern of mosaic evolution in which the internal and external anatomy are giving off different signals."
The researchers examined specimens from Invertebrate Paleontology collections at the Museum of Comparative Zoology (MCZ) and the Smithsonian Institution. The study was funded in part by the MCZ Wetmore Colles Grant.
The study was featured in the Nature Portfolio Ecology & Evolution Blog.