Freshwater Jellyfish

The freshwater jellyfish is a small hydrozoan, native to the Yangtze River basin in China but now spread through still lakes, ponds, reservoirs, and quarries on every continent except Antarctica. Its bell-shaped medusa stage grows only about 20 to 25 millimeters across and carries up to 400 fine tentacles armed with stinging cells strong enough to paralyze the water fleas and copepods it feeds on but too weak to trouble human skin. It begins life as a tiny polyp that can bud off medusae during warm months and survive winter as a dormant, resistant podocyst, letting the species spread to new waters when those resting stages are carried along by birds, boats, or currents.