A joint group of researchers from the University of Padua and the University of Trieste has observed surprising behaviours in jellyfish of the Aurelia species, commonly known

as the four-leaf clover jellyfish. The results of the study, published in the prestigious journal Behavioural and Brain Sciences, raise fascinating questions about the origin of curiosity and the possibility that forms of cognition can emerge even in the absence of a centralised brain.

‘Our results are particularly interesting,’ explains Cinzia Chiandetti, professor of cognitive neuroscience at the Department of Life Sciences of the University of Trieste, ‘because these animals are considered ‘brainless’: their nervous system is organised radially, without a command centre, and equipped only with rudimentary sensory organs. Finding signs of memory and attraction to novelty in them is an important key to understanding the evolution of nervous systems and cognition itself.’

Specifically, the researchers observed the behaviour of young jellyfish placed individually in a rectangular tank. In the first phase, each animal was presented with an object, which elicited an immediate reaction: the jellyfish left the empty part of the tank and headed towards the novelty. In the second phase, after a one-minute interval, a second object was placed alongside the first, and on that occasion, the jellyfish showed a clear preference for the latter. This behaviour, which experts call ‘neophilia’, indicates that jellyfish have a memory of the first object and are attracted to the new one.

‘Not only did the jellyfish show neophilia,’ comments Christian Agrillo, professor of comparative psychology at the University of Padua, ‘but they also showed that they could retain certain information in their memory for at least one minute. We generally think that in the sea they approach us passively, carried by the current. Our study also opens up the possibility that in some cases they do so because of the same attraction to novelty documented here. You could say that perhaps they are curious to get to know us!’

The study invites us to rethink traditional models that link cognition to the presence of centralised brains, suggesting that even ‘diffuse’ nervous systems, such as that of jellyfish, can support complex behaviours. This discovery once again pushes the boundaries of what we think is possible in the animal world.

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