Jellyfish are very simple sea creatures that have lived in the oceans since before the time of the dinosaurs. Found in every ocean around the world, some jellyfish live in deep, cold water, while others prefer warm, shallow coastal waters. Scientists believe jellyfish have been around at least 500 million years.
Members of the scientific phylum Cnidaria, jellyfish are considered to be plankton and are closely related to sea anemones and corals. Since jellyfish aren't really fish, many scientists prefer to call them "jellies" or "sea jellies" instead.
Jellyfish consist of three basic layers. The outer layer, called the "epidermis," contains the nerve net.
The middle layer is made of "mesoglea," the thick, elastic stuff that looks like jelly. The final, inner layer is called the "gastrodermis."
Inside their bell-shaped bodies, jellyfish have a large “mouth" where food comes in and waste goes out. Jellyfish eat fish, shrimp, crabs, small plants, and sometimes even other jellyfish. They squirt water from their mouths to move themselves through the water.
Jellyfish don't purposefully attack humans. Most jellyfish stings occur when someone accidentally touches a jellyfish. Even a dead jellyfish can sting!
How harmful a jellyfish sting is depends on the type of jellyfish. Some jellyfish stings have little or no effect on humans, while others may cause minor discomfort to extreme pain.
WONDERful jellyfish facts:
- A group of jellyfish can be called a "bloom," a "swarm," or a "smack."
- The lion's mane jellyfish might be the longest animal in the world. Its thin tentacles can reach up to 120 feet long.
- The Nomura's jellyfish might be the largest jellyfish. Average specimens weigh 330 pounds, and the largest can reach 440 pounds.