June 06, 2025 - "Go, don't eat my brain." There is hardly anyone who has not heard this phrase. In our language, "eating the brain" is used merely as an idiom, but there is a species in the ocean that actually eats its own brain. This species is called the "Sea Squirt." Sea squirts were once considered marine plants because they are fixed in one place at the bottom of the ocean and filter water to obtain nutrients from it. But when scientists studied the complete life cycle of these "plants," they discovered that they are not plants but animals. When they are in the larval stage, they swim around in the form of fish-like tadpoles. Their bodies contain all the basic structures found in vertebrates, such as a brain, spinal cord, blood circulatory system, backbone, digestive system, anal opening, and reproductive organs. However, upon reaching maturity, these tadpoles plant their feet on the ocean floor and confine themselves to one place. After this, all those organs of their body begin to waste away which are not important for the remainder of their life. Animals mostly need a brain to control their movements. Animals that remain fixed in one place for their entire life and cannot move do not need a brain. The brain and nervous system did not evolve in plants precisely because they have no need for a brain and nervous system. Processing in the neurons of the brain requires a lot of energy. an organ that consumes a large amount of energy but provides no benefit is lost very quickly in the evolutionary process. A mature sea squirt does not have separate males and females; instead, every sea squirt is simultaneously both male and female. In other words, every sea squirt produces both sperm and eggs. These eggs and sperm are released into the water, where the eggs are fertilized by the sperm. The fertilized eggs scatter here and there in the water, where in just one or two days, tadpoles emerge from them and begin to swim, and thus their life cycle continues. In this graphic, you can see mature sea squirts attached to the ocean floor, along with the body plan of a sea squirt tadpole showing all the structures found in vertebrate animals.