Chelicerate neural ground pattern in a Cambrian great appendage arthropod

Area of Science:

• Paleontology
• Neuroscience
• Evolutionary Biology

Background:

• Preservation of neural tissue in early Cambrian arthropods allows for detailed study of their nervous systems.
• Understanding arthropod neuroanatomy is key to resolving controversies regarding the segmental identities of fossil taxa.

Purpose of the Study:

• To document the neuroanatomy of Alalcomenaeus sp., a 'great appendage' arthropod from the Chengjiang biota.
• To provide the most complete neuroanatomical profile of a Cambrian animal to date.
• To compare the neuroanatomy of Alalcomenaeus with extant arthropods to infer evolutionary relationships.

Main Methods:

• Micro-computed tomography (CT) was used to visualize the neuroanatomy of Alalcomenaeus.
• Detailed analysis of the brain, ganglia, and optic neuropils in the head and trunk.
• Comparative analysis with the nervous systems of extant arthropod groups.

Main Results:

• Alalcomenaeus exhibits a nervous system configuration most similar to Chelicerata, with one optic neuropil, a protocerebrum, four head ganglia, and eight trunk ganglia.
• The great appendage is innervated by the deutocerebral neuromere, suggesting homology with chelicerae.
• Both Chelicerata and Mandibulata brain configurations were present by the early Cambrian.

Conclusions:

• The neuroanatomy of Alalcomenaeus supports its placement within the chelicerate total group.
• The study provides strong evidence for the homology between the 'great appendage' and the chelicera.
• Early Cambrian arthropods already possessed the two major brain architectures seen in modern arthropods.