rhopalium

physiology

Also known as: rhopalia

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July 13, 2026

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The term "rhopalium" refers to a marginal sensory organ found in some jellyfish. These club-shaped structures are crucial for jellyfish to detect environmental cues such as changes in light and gravity, aiding in navigation. Jellyfish, unlike animals with centralized brains, possess a nerve net, a diffuse system of nerve cells that coordinates responses to stimuli. The rhopalia are part of this system, enabling jellyfish to interact with their environment without a brain.12

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nervous system
Diffuse nervous systems
…be arranged sensory bodies, called rhopalia, which contain ganglionic concentrations of neurons. In the sea anemone Metridium some of the nerve fibres are 7 to 8 mm (0.3 inch) long and form a system for fast conduction of nerve impulses. Such specializations may have allowed the evolution of different functions.…
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…be arranged sensory bodies, called rhopalia, which contain ganglionic concentrations of neurons. In the sea anemone Metridium some of the nerve fibres are 7 to 8 mm (0.3 inch) long and form a system for fast conduction of nerve impulses. Such specializations may have allowed the evolution of different functions.…
Read More