The Caribbean box jellyfish, which doesn’t have a brain, can alter its behavior based on past experiences.

https://www.science.org/content/article/no-brain-no-problem-jellyfish-learn-just-fine?utm_campaign=SciMag&utm_source=Facebook&utm_medium=ownedSocial&fbclid=IwAR1y-taGZkr9HOdXdTpo-uIlHeW-9Ww7dukatvTaCvoIxRNXcSPMQ_USFfk