Is it true that jellyfish don't have a brain?

June 18, 2025 - Jellyfish, inhabiting seas and oceans, often attract interest from scientists and nature enthusiasts due to their unusual anatomy. One of the most common questions about them is: do jellyfish really lack a brain? This article examines scientific facts related to the anatomy and behavior of jellyfish.

Jellyfish anatomy: absence of a central brain

Jellyfish belong to the phylum Cnidaria, which includes about 10,000 species of marine animals. Scientists, such as Dr. Anna Petrova from the Institute of Oceanology of the Russian Academy of Sciences, confirm that jellyfish do not have an organ that could be classified as a brain. Instead, they have a diffuse nervous system consisting of a network of nerve cells distributed throughout the body. This system allows jellyfish to respond to external stimuli such as light, temperature, or the presence of prey.

According to a study published in the Journal of Experimental Biology in 2023, the nervous system of jellyfish consists of neurons forming a so-called nerve net. It provides basic reflexes, such as body contractions for swimming or reaction to touch. However, complex processes such as memory or decision-making are absent in jellyfish.

How do jellyfish function without a brain?

Despite the absence of a central brain, jellyfish demonstrate amazing abilities. For example, box jellyfish (Cubozoa) have a complex visual system with 24 eyes that allow them to navigate in space and avoid obstacles. A study conducted at the University of Copenhagen in 2024 showed that these jellyfish use their eyes to detect prey and navigate in murky waters.

Jellyfish movement is also coordinated through the nerve network. For example, the rhythmic contractions of their bell that enable swimming are regulated by signals from nerve cells. Dr. John Smith, a marine biologist from the University of California, notes: "Jellyfish demonstrate that complex behavior doesn't always require a complex nervous system. Their simplicity is an evolutionary advantage."

Evolutionary role of the absence of a brain

The absence of a brain in jellyfish is explained by their evolutionary adaptation. Jellyfish appeared about 600 million years ago, making them one of the oldest multicellular animals on Earth. Their simple anatomy has allowed them to survive in diverse conditions, from tropical seas to cold Arctic waters.

Professor Maria Gonzalez from the University of Barcelona emphasizes: "Jellyfish don't need a brain, as their lifestyle doesn't require complex information processing. Their nervous system is perfectly suited for performing basic functions such as feeding and movement."

Conclusion

Although jellyfish don't have a brain in the traditional sense, their nervous system allows them to effectively interact with the environment. Modern research continues to reveal amazing features of these animals, confirming that the absence of a brain doesn't prevent jellyfish from being successful ocean inhabitants. Further research, planned for 2026 as part of the international OceanMind project, may shed light on the evolution of nervous systems in cnidarians.