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They come in many shapes, sizes, and colors, but jellyfish are found in every ocean in
the world.
If there's saltwater - whether it's warm tropical seas or frigid polar waters - jellyfish are
there!
Jellyfish belong to a large group of animals called cnidarians.
Cnidarians are one of the most common types of sea animals with more than 10,000 species.
Along with jellyfish, cnidarians include sea anemones, corals, sea fans, and freshwater
hydras.
The smallest jellyfish may only reach about the size of your thumbnail.
The largest jellyfish, the lion's mane jellyfish, may reach a size of 7 feet or 2.3 meters across,
with tentacles 121 feet or 37 meters long.
Jellyfish are invertebrates.
That means they do not have backbones.
In fact, jellyfish have no bones at all!
They don't have eyes, ears, hearts, or brains either.
Unlike fish, jellyfish have no gills.
Instead, they absorb oxygen through their skin.
Jellyfish also swim in a way that is very unlike how fish swim.
Jellyfish use a simple type of jet propulsion to get around: they open their body like an
umbrella and then close it.
By contracting their body, the water inside is forced out and the jellyfish moves forward.
Constantly moving is the only thing keeping jellyfish afloat, but even with this effort
they can be easily pushed around by strong winds or ocean currents, which is what leads
some jellyfish to be washed up on beaches.
The top of a jellyfish is called the bell, and their jellylike bodies are made almost
entirely of water - about 95%.
Depending on the species of jellyfish, they may also have frilly oral arms or long tentacles.
Some jellyfish have light sensors, called eye spots, that can sense sunlight and help
the jellyfish know which way is up, and some jellyfish are bio-luminescent, which means
that they can produce light from their bodies, kind of like a firefly.
Although no one knows for certain why they light up, scientists believe it to be a defense
mechanism, to startle a predator away, or perhaps to attract another predator to eat
their attacker.
Jellyfish are largely transparent, which means you can see through them.
This makes them difficult to see in the water, which helps them hide from predators that
would like to eat them, like sea turtles, sharks, swordfish, and even other jellyfish.
Jellyfish are carnivores themselves, but they do not hunt their prey.
They wait for fish or other small animals to get caught in their tentacles.
The tentacles are covered in stinging cells which burst and inject venom into their prey,
paralyzing it.
Jellyfish can also sting humans, and while some jellyfish stings are just painful, some
types of jellyfish can deliver a sting that can kill.
Jellyfish have a complex and interesting life cycle.
Usually, they begin as eggs, floating in the ocean currents.
Each egg will then develop into a planula: a swimming larval form.
After a few days, the planula will find something sturdy to anchor itself to and undergo a transformation
into a polyp.
Polyps look a bit like underwater flowers, using their tentacles to catch and eat zooplankton.
Eventually the polyps begin to bud, splitting off into an ephyra, or immature jelly, which
then develops into a medusa, the form we usually recognize as a jellyfish.
Despite all of the time it took to get there, a mature jellyfish usually only lives up to
about a year.
Distinctive and often beautiful, jellyfish may seem like calm and peaceful ocean creatures.
Although some types of jellyfish are harmless, others are dangerous predators that can prove
painful or even deadly to those who venture too close.
I hope you enjoyed learning about jellyfish today.
Goodbye till next time!