Jellyfish are among the oldest animals on Earth, drifting through the oceans for over 500 million years, long before dinosaurs existed. Despite their name, they aren’t fish at all. They’re simple, gelatinous creatures made up of about 95% water, with no brain, heart, or bones.

Jellyfish move by gently pulsing their bell-shaped bodies, pushing water behind them like a natural jet engine. Their long tentacles are lined with stinging cells called nematocysts, which inject venom to capture prey such as plankton, small fish, and eggs. Some species have mild stings, while others, like the box jellyfish, are extremely dangerous to humans.

Instead of a brain, jellyfish use a basic nerve net to sense light, touch, and chemicals in the water. This simple system has been effective for hundreds of millions of years, proving that complex organs aren’t always necessary for survival.

In recent years, jellyfish populations have surged in some coastal areas. Warmer seas, overfishing of their predators, and nutrient pollution create ideal conditions for massive “blooms,” which can clog fishing nets, damage power plant intakes, and disrupt tourism.

Jellyfish may look delicate, but they are remarkably resilient. One species, Turritopsis Dohrnii, is often called the “Immortal Jellyfish” because it can revert to its juvenile form after reaching adulthood, essentially restarting its life cycle.

Silent, ancient, and strangely beautiful, jellyfish are living reminders of how life can thrive with the simplest of designs.