The cabbage-head jellyfish, more commonly known as the cannonball jellyfish, lives in warm, temperate estuary waters around the world. They are commonly found along the North American Atlantic seaboard, but also live in areas of the Pacific.
The cannonball jellyfish lives in waters that average 73.6 degrees Fahrenheit. It is named for the distinct shape of its bell, which can reach up to 10 inches in diameter. Though this species does not possess the long tentacles of other cnidarians, it can secrete a toxin when disturbed; the sting of a cannonball jellyfish is usually harmless to humans, though in severe cases it can cause cardiac problems.