Cambrian origin of the arachnid brain

Area of Science:

• Paleontology
• Neuroscience
• Evolutionary Biology

Background:

• The Cambrian period witnessed rapid arthropod diversification.
• Mollisonia and Sanctacaris were previously considered basal chelicerates.
• Understanding early arthropod neuroanatomy is key to their evolutionary history.

Purpose of the Study:

• To investigate the neuroanatomy of Mollisonia symmetrica.
• To re-evaluate the phylogenetic position of Mollisonia based on neural traits.
• To understand the evolution of arthropod brains.

Main Methods:

• Analysis of preserved neuronal tissues in Mollisonia symmetrica fossils.
• Comparative neuroanatomical analysis with extant and fossil arthropods.
• Phylogenetic analyses incorporating neural characteristics.

Main Results:

• Mollisonia symmetrica exhibits a reversed brain organization compared to merostomes.
• A distinct deutocerebrum is identified, connected to chelicerae.
• Proso- and protocerebral domains are folded caudally, interacting with appendicular neuromeres.

Conclusions:

• Mollisonia symmetrica represents an upper stem arachnid, not a basal chelicerate.
• The findings necessitate a revision of early euarthropod brain evolution.
• This lineage may have given rise to successful arachnidan predators.