Caribbean box jellyfish are built with two major components: the rhopalial and ring nervous system, otherwise described as a dispersed central nervous system. Meaning they lack a brain. So, how do these jellyfish retain information and engage in learning how to hunt, hide, breed, and live? Tests on this Jellyfish have recently shown that they can retain and learn from trial and error without a central nervous system. They prove that even without a brain, the box jellyfish are more intelligent than they seem and aren’t some squishy floating object.
The Caribbean box jellyfish (Tripedalia cystophora) is mainly found in tropical warmer waters, floating between mangrove roots in lagoons where they hunt tiny crustaceans. The Jellyfish is a translucent brown/yellow color. It is usually 1cm in diameter and has emerged from the four corners of the bell’s three tentacles. These tentacles are aligned with small bumpy nematocysts, a sensory organism that delivers a sting to predators.
Although these creatures don’t look like a lot they sure can see a lot and have a complex visual system. The main body of the jellyfish is known as a bell. Attached to 4 corners of the bell, the tentacles consist of 6 eyes, a total of 24 eyes, each with a different purpose (Wikimedia Foundation. 2023, September 23). One set contains large medial eyes with spherical lenses, another a pair of slit eyes, and lastly, pit eyes. These different eyes help them navigate obstacles and a visual tuning behavior, allowing them to avoid predictors and change swimming patterns. It also allows specific types of light to come into the eye, helping them when waters get murky due to tide changes or pollution (Wikimedia Foundation. 2023, September 23). Recent studies have discovered that through this complex visual system, they can retain information, helping them remember things even without a brain.
In a study held by Current Biology on October 9th led by Dr. Anders Garm, these scientists conducted an experiment where they placed some Caribbean box jellyfish in an aquarium. This aquarium is designed to have white and gray stripes around the border (Figure 1). The gray stripes would be able to be detected by the jellyfish and mirror a mangrove root as they try to avoid colliding with them when hunting for crustaceans. After the first 7 minutes, it was reported that the jellyfish swam fairly close to and often bumped into the stripes. When it ran into stripes the Jellyfish received both visual and mechanical stimulation from bumping into the obstacles (Bielecki et al. 2023).
The Scientist changed the lab slightly by replacing the strips with solid gray fields. This proved more challenging as the jellyfish continually ran into these fields. Finally, scientists mimicked the neurological response the tentacles give out, creating a pulsing motion that usually propels them when swimming. Scientists severed the tentacles and isolated them from the bell while they moved around the gray lines representing the mangroves (Figure1). This created the sight of the jellyfish remaining still. Here, they found that sending a weak electronic signal to the visual sensory system would eventually start to send the signal itself when it gets too close to the gray and white lines (Bielecki et al. 2023).
This lab’s results achieved behavior relevant to what would happen in the wild. “Both visual stimulation and mechanical stimulation is something that (occurs) in their natural habitat,” he said. “They know exactly what to do with this,” says Dr. Michael Abrams, a researcher in the Department of Molecular and Cell Biology at the University of California, Berkeley. In conclusion, Dr. Abrams decided that ‘these jellyfish can retain information. There is “evidence of some amount of short-term memory”(Schnuer, J. 2023) present in this species and that these animals are smarter than we thought.
References
Schnuer, J. (2023, September 25). Surprising jellyfish finding challenges what’s known about learning and memory. CNN. https://www.cnn.com/2023/09/22/world/jellyfish-brain-central-nervous-system-learning-scn/index.html
Bielecki et al., Associative learning in the box jellyfish Tripedalia cystophora, Current Biology (2023), https://doi.org/ 10.1016/j.cub.2023.08.056
Wikimedia Foundation. (2023, September 23). Tripedalia Cystophora. Wikipedia. https://en.wikipedia.org/wiki/Tripedalia_cystophora
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