What is Largest living creature without a brain?

The largest living creature without a brain is the blue whale (Balaenoptera musculus), which can grow up to 100 feet long and weigh as much as 200 tons. However, it's important to clarify that blue whales do have brains; instead, the title of the largest creature without a brain goes to the jellyfish. Certain species of jellyfish, like the lion's mane jellyfish, can reach impressive sizes, with some individuals having tentacles that span over 100 feet. These creatures lack centralized brains and instead possess a simple nerve net for processing information.