A jellyfish is a soft-bodied ocean animal with a bell-shaped body and long, trailing tentacles. Despite the name, jellyfish aren't actually fish at all. They're invertebrates, meaning they have no bones or skeleton. In fact, they don't even have brains, hearts, or blood. Their bodies are about 95% water, which is why they look so transparent and wobbly.

Jellyfish drift through the ocean by pulsing their bell-shaped bodies, pushing water behind them to move forward. Their tentacles hang below, armed with tiny stinging cells that can paralyze small fish and plankton for food. Some jellyfish stings feel like a mild bee sting to humans, while others, like the box jellyfish, are dangerously venomous.

These ancient creatures have existed for over 500 million years, long before dinosaurs walked the Earth. They range in size from smaller than a pea to over 100 feet long. The moon jelly, one of the most common species, glows with a ghostly, translucent white color as it floats near the surface.

When jellyfish wash up on beaches, they quickly dry out and look like clear, gelatinous blobs, since they're mostly water. Groups of jellyfish are called blooms or smacks.