A groundbreaking discovery regarding the ancient creature Mollisonia has emerged from recent research, suggesting that arachnids, including modern spiders, originated in ocean environments. This discovery upends the long-held belief that these animals developed traits for life on land only after they adapted to terrestrial habitats.
Mollisonia lived more than 500 million years ago in what is known as the Cambrian period. It looks very similar to other early chelicerates from the lower and mid-Cambrian. Researchers at the Museum of Comparative Zoology at Harvard University took a very close look at its fossilized remains. To their amazement, they found an exquisitely preserved brain and nervous system. By looking at the comprehensive structure of Mollisonia’s brain through novel imaging techniques, researchers were able to identify critical aspects of its evolutionary history.
The creature’s body was composed of two main parts: a broad rounded “carapace” at the front and a sturdy segmented trunk that concluded with a tail-like structure. That anterior portion, known as the prosoma, has a radially arranged array of segmental ganglia. These ganglia are capable, in real time, of orchestrating the movement of five pairs of appendages. This unique configuration shows its primitive character as a basal chelicerate. It even predates the most recent common ancestor of all horseshoe crabs.
Mollisonia’s brain is organized in a way that differs from modern crustaceans, insects, and the centipede. Its anatomy is laid out just like today’s spiders and their relatives, the three segmented body plan now found in arachnids. This type of neural configuration is even more similar to that of arachnids than it is to horseshoe crabs. This resemblance indicates a much stronger evolutionary relationship between Mollisonia and today’s arachnids.
Those results indicate that Mollisonia is more closely related to modern arachnids than to the horseshoe crab. This biological link implies that its evolutionary heritage was instrumental in the early emergence of clades like that of spiders, scorpions, sun spiders, vinegarroons, and whip scorpions. The research is the first to demonstrate that arachnids were among the first organisms to make their way onto land. This innovative gesture probably triggered the development of insect wings, originating flight and better escaping tactics.
Mollisonia’s unusual neural architecture is helping researchers to predict the common genetic blueprint found throughout all arthropods. This finding extends our understanding of how complex nervous systems evolved independently in many lineages. It highlights the important part ocean environments had in the early development of arachnid evolution.