Jellyfish Have No Brain, Heart, or Blood

Jellyfish are among the planet"s simplest multicellular organisms. They have no brain, heart, blood, or bones. Their bodies are 95% water. Instead of a central brain, they use a diffuse nerve net. This net senses light, responds to danger, and coordinates contractions. How do they live without a heart and blood? Their bodies are thin enough that oxygen diffuses directly into cells. Nutrients spread the same way. This primitive design has worked for 500 million years - they existed long before dinosaurs and are still here. Source: Marine Biology Review