Comb Jelly's Complex "Brain-Like" Organ Reshapes Understanding of Early Animal Evolution
A recent study indicates that comb jellies, ancient gelatinous creatures present in oceans for approximately 550 million years, possess a central sensory organ that is more complex and brain-like than previously recognized. This finding has implications for understanding the evolution of animal nervous systems, particularly since comb jellies are considered among the oldest blueprints of early animals. The discovered complexity suggests that brain-like structures may have been a part of animal life for an extended period.
Pawel Burkhardt, an evolutionary biologist at the University of Bergen in Norway and senior author of the study, stated that the research significantly advances the understanding of behavioral coordination evolution in animals.
Key Details of the Discovery
The leap in understanding resulted from high-resolution 3D scans of the comb jelly's aboral organ (AO), using an advanced imaging technique called volume electron microscopy.
- The AO is a sensory structure that helps the jelly orient itself by detecting gravity, pressure changes, and light direction.
- The scans digitally reconstructed the organ, revealing a complex structure distinct from equivalent organs in cnidarians (like jellyfish) or bristle worm larvae.
- The jelly's nerve net converges into a dense central node that encases the AO, with synapses facilitating electrical information transmission.
- The AO contains about 900 cells, comprising 17 distinct cell types, 11 of which are newly identified.
- Anna Ferraioli, a molecular biologist at the University of Bergen and the study's first author, noted the morphological diversity of the AO cells.
- Many non-synaptic cells within the AO were observed to contain vesicles, suggesting their involvement in volume transmission, a slower form of chemical signaling.
- The genes and molecules involved in forming this elementary central nervous system are unique to comb jellies, differing from those in cnidarians and bristle worm larvae.
The researchers concluded that the ctenophore AO functions as a distinct, integrated, and potentially multimodal sensory system crucial for behavioral regulation. Anna Ferraioli explained that the AO serves as the comb jelly's brain.
Pawel Burkhardt added that this suggests centralized nervous systems have evolved independently multiple times, implying their emergence in animal anatomy earlier than previously thought, albeit in varied forms.
The research was published in the journal Science Advances.