Jellyfish aren’t fish at all. Instead, they’re what marine biologists call gelatinous zooplankton.
Their bodies are made of up to 95% water. This means that jellyfish fossils are a bit rare. However, scientists estimate that they’re between 400 and 700 million years old.
That means they are older than dinosaurs!
There are an estimated 10,000 species of jellyfish swimming in Earth’s oceans today.
They range in size from the tiny Irukandji Jellyfish, which can be as small as 1 centimetre (0.39 inches) in diameter, to the massive Lion’s Mane jellyfish, which can have tentacles stretching 27 meters (88+ feet) long!
And jellyfish completely ignore the rules with their anatomy too!
They have no head, heart, lungs, or brain! However, a few jellyfish have eyes — such as the deadly Box jellyfish.
They can even clone themselves as polyps (baby jellyfish), creating additional jellyfish that are genetically identical.
Today, most scientists refer to a group of jellyfish as either a swarm or a bloom. A swarm is a gathering of jellyfish, while a bloom results from rapid reproduction.
We think the older name for a group of jellyfish — a smack — is a lot more fun, though!
Jellyfish eat small fish, crabs, shrimp, and aquatic plants by stinging them using cells in their tentacles called cnidocytes and nematocysts.
Then, they use their tentacles to bring their stunned or poisoned prey toward the opening on the underside of their bell — the dome-shaped upper part of their body.