A jellyfish can almost entirely vanish if it washes up on a hot beach because it is 95% water.

Jellyfish belong to the phylum Cnidaria and are composed of about 95% water and 5% organic matter. Unlike mammals, which are roughly 60% water, jellyfish lack a rigid skeletal structure or a protective outer skin to prevent fluid loss. They rely on hydrostatic pressure to maintain their structural integrity and move through the ocean.When a jellyfish is removed from the water and exposed to direct sunlight, a process called desiccation begins almost immediately. Because they lack a waterproof membrane, the water within their mesoglea—the jelly-like substance between their epithelial layers—evaporates rapidly. This causes the organism to lose its volume until only a tiny fraction of its original mass remains as a faint residue on the sand.Research from institutions like the Monterey Bay Aquarium Research Institute highlights that even a dead, evaporated jellyfish can be hazardous. The nematocysts, or stinging cells, are mechanical structures that do not require the animal to be alive to fire. These microscopic harpoons can remain pressurized and functional for several days after the jellyfish has dried out on a beach.Oceanographers have noted that large blooms of jellyfish, known as 'smacks,' can lead to massive strandings during specific tidal events. In these cases, thousands of jellyfish may disappear from a shoreline in a single afternoon due to high temperatures. This rapid evaporation is a unique biological trait that makes jellyfish one of the most fragile yet resilient creatures in the marine ecosystem.