EXACTLY ARE JELLYFISH?
semi-transparent, graceful creatures. They are only five percent solid matter and form, and the remaining 95 percent is all water!
Sea anemones and corals are related to jellyfish; they belong to the
same phylum (cnidaria).
Cnidaria (pronounced ny-DAIR-ee-ah)
Number of Jellyfish
Sizes: Jellyfish come in a wide variety of sizes and shapes, from the 1" thimble size Caribbean jellyfish to the Arctic Lion's Mane's jellyfish with tentacles as long as 100 feet, and weighing up to a ton.
"If I Only Had a Brain..." or a backbone, heart, bones, or blood, for that matter: Jellyfish do not have a brain, but an elementary nervous system capable of detecting and responding to light, smell and other stimuli. Being invertebrates, they lack a spine.
Habitat: Most live in shallow coastal waters, but some inhabit depths of 12,000 feet! There are
also some freshwater jellyfish.
Brilliant Colors: Jellyfish colors are known for great brilliance...blue, orange, red, and more.
Polymorphism: Jellyfish can exist as two different types of species in one life time. Part of the time they can exist as polyps and part of the time as medusa.
Lifespan: Three to six months.
Locomotion: Jellyfish drift with the currents with little control over horizontal movement, although there is some ability to navigate vertically.
Sting/Venom: Poisonous, venom-filled barbs called nematocysts —in
some cases thousands of them—line jellyfish tentacles. The venom
paralyzes its victims, although it is usually only strong enough to
paralyze small creatures. A few species, like the box jellyfish of
Australia, can be very dangerous to humans. Beachcombers
should also beware of dead jellyfish (of any kind) that wash ashore,
as their tentacles can still be active.
baby jellyfish isn't an easy job, but somebody has to do it. Almost
unnoticeable amid a sea of artwork that covers the wall, a small
door opens into the guts of the new jellies exhibit at the
Monterey Bay Aquarium. It's where Bruce Upton does the essential,
but not glamorous, work of raising jellyfish.
Caution: If you or someone gets stung by a jellyfish, make sure to get them out of the water to avoid drowning. Alcohol should not be put on stings as it actually stimulates the venom.
Aggressive Jellyfish?: Jellyfish do not attack humans (they can't direct their horizontal movement), but drift into them, and humans get entangled in their tentacles.
Jellyfish belong to
the phylum Cnidaria, whose members possess stinging
cells that can inject a paralyzing poison into prey.
Other members of this phylum include sea anemones, sea fans,
hydra and reef-forming corals. True jellyfish fit into
the species scyphozoa; most have an umbrella shaped
concave body with a centrally located mouth. The cells
that line the inner part of the jellyfish body cavity
secrete digestive enzymes and absorb nutrients. The
fossil record for cnidarians begins in the Pre-Cambrian
(earliest) era of earth history, meaning that the direct
ancestry of these creatures dates to at least 600 million
In the depths of the ocean lurks a huge, predatory
jellyfish, recently caught in the Monterey Submarine Canyon
(a 4000-meter trench off of the California coast). The dark
red creatures are 2 to 3 feet long, and roam waters that
rarely get above 40 degrees Fahrenheit. Most surprisingly,
in place of tentacles, they have a few short, thick arms
that may be used for feeding. Though Big Red had been
discovered and photographed a few years ago, scientists only
recently obtained a specimen for study. They currently know
almost nothing about it, but hope to learn more in the
coming months. Get the details and photos at
jellyfish can see, man.
The box jellyfish, known for their square-shaped bodies, are
more sophisticated than most jellyfish species. Not only
can they swim better, but recently scientists discovered
that 8 of their 24 eyes function extremely well. Each eye
contains a lens and a retina, providing a blurred vision
that allows the animal to focus on large objects. This form
of vision works well in the near shore waters, among
mangrove roots and other obstacles, that box jellyfish
populate. Read more at
Okay, so not only can box jellyfish see, but one species is
tailor-made to attack and kill vertebrates. The box jelly
found off the coast of northern Australia, has perhaps the
most deadly venom in the word. Sixty-five Australians have
been killed by it in the last 50 years. While many
jellyfish species float freely and feed on plankton, these
predators swim fast and can kill fish and other animals with
“a single flick of a tentacle”. Their tentacles can grow to
nearly seven feet long, so they are a definite danger to
swimmers. More from
Natural History magazine.
What do you know about
our quiz to learn more about these cool drifters!