Out of the 8.7 million animal species, only a few do not have brains. Some, like leeches, have 32 brains, while some, such as jellyfish, do not have one at all. One might wonder, how do jellyfish function without a brain? Do they know of their existence? And how do they catch prey? In this article, I will be breaking down jellyfish. (nhm.ac.uk)

The name ‘Jellyfish’ describes the sea animal perfectly. It has a jelly-like structure, even though it is not a fish. Not only do jellyfish not have brains, but they also do not have organs in the traditional sense. These animals are known as invertebrates, meaning they lack any complex organs and a backbone. So, how do jellyfish function if they do not have brains? Well, to make up for lacking a centralized brain, they navigate and react to their environment using a decentralized ‘nerve net’ or ‘nerve ring.’ No, a nerve net is not the tentacles; instead, they are a mesh-like network of interconnected neurons that form the nervous system and are located underneath the bell, which is the half-dome-like top of the jellyfish. The nerve net allows them to sense and respond to stimuli like light, vibrations, touch, and currents. This allows them to enable behaviors like capturing prey and swimming.

Now, in order to detect the prey, they have light-sensitive cells around their bell called rhopalia. This gives them a blurry sense of what is in front of them, which is how they differentiate prey from other organisms. Here comes the fun part: capturing! Once the rhopalia detect that it is prey, the translucent animal uses its stinging cells called the nematocysts (the tentacles) to paralyze the prey with venom before their oral arms guide the prey to their ‘stomach,’ gastrovascular cavity, which is a fancy way of saying a two-way digestive system. By now, the enzymes in the cavity take over, and the nutrition is absorbed. And no, they do not have an anus; any undigested remains are expelled through the mouth (europe.oceana.org). Alyssa Smith (10) says, “Thankfully, they do not have a brain; the process of having undigested remains come back out through the mouth must be an unpleasant experience.”

This also leads to the conclusion that, sadly, jellyfish do not know of their existence. Tina Jin (10) comments, “How interesting; they float around for a few years not knowing of their existence, do what they have been doing for centuries, and pass.” So while other animals can process and experience emotions, jellyfish and many others can not. They are animals that are so complex, yet so simple.