Jellyfish Myths Explained (Fact vs. Fiction)  

Not many critters give folks the heebie-jeebies quite like jellyfish.

They’re boneless, for starters, and a lot of people seem to just have a general bias toward invertebrates. They look particularly alien, and sport stinging tentacles and oral arms.

And their presence, or imagined presence, can put a damper on our enjoyment of a pretty much universally loved hangout zone: the ocean beach.

As with so many potentially dangerous organisms, though, jellyfish overall get an unfairly bad rap, and are also tagged with quite a lot of misinformation.

So let’s bust some of the most common jellyfish myths floating around out there — and explore some facts that sound too wild to be true, but are.

The more you know about anything, the less you need to blindly fear it—and that very much applies to sea jellies!

In this article, we’ll do our best to dispel some of the most widespread jellyfish myths—and, just for good measure, tell you about some strange-but-true facts about these remarkable creatures.

6 Most Common Jellyfish Myths

Let’s run through some of the most oft-repeated jellyfish myths that muddy the waters, if you will, when it comes to understanding one of the most infamous members of the marine ecosystem.

Myth #1: Jellyfish Are Fish

I mean, it’s in the name, right?

Well, as with so many, many common labels for living things, “jellyfish” is a definite misnomer. Jellyfish aren’t fish at all.

Fish are vertebrates, for one thing, while jellyfish are invertebrates.

The simplest swimming animals, they belong to the wide-ranging taxonomic phylum Cnidaria, which also includes such critters as sea anemones, corals, and hydrozoans.

Many scientists prefer to call jellyfish “sea jellies,” to avoid the whole fish confusion altogether.

Myth #2: The Portuguese Man-o’-War and By-the-Wind Sailor Are Jellyfish

Depending on your perspective, this could either be myth or fact.

Technically speaking, the vividly colored, surface-floating cnidarians known as the Portuguese man-o’-war—which boasts extravagantly long tentacles—and the related by-the-wind sailor or velella, which has much shorter tentacles, are not true jellyfish, even though they exhibit a strong physical resemblance.

That is, they don’t belong to Class Scyphozoa, the “true jellies,” nor to the box-jellyfish Class Cubozoa.

In fact, the Portuguese man-o’-war and probably the by-the-wind sailor as well (there’s some debate) are not single discrete animals but rather colonial organisms made up of many tiny polyps or zooids specialized for different functions but linked together by a common digestive tract.

That’s a big biological difference from true jellyfish and box jellyfish.

OK, but you could actually still argue that it’s acceptable to refer to Portuguese man-o’-wars and by-the-wind sailors as jellyfish.

That’s because some scientists use the term “jellyfish” to describe the free-swimming medusa stage that’s part of the complex lifecycles of many cnidarians, not just true and box jellies.

In other words, this way of thinking considers “jellyfish” as a catchall category of body form or biological blueprint—that of a free-swimming tentacled entity—rather than a taxonomic group.

Myth #3: All Jellyfish Are Deadly

Far from true!

While all jellyfish possess stinging cells—nematocysts—few are truly life-threatening to people.

The stings of many jellyfish, such as the common and widespread moon jelly, barely register, if at all, to human beings. Other stings are painful to some degree, but aren’t actually dangerous—just bothersome.

There are indeed a few kinds of sea jellies that pack a real punch when it comes to their sting, most notoriously various box jellies, such as the sea wasp of the Indo-Pacific, perhaps the most feared jelly of all, and the various, remarkably little Irujandji jellyfish.

It’s important to stress that some people can have allergic reactions to even garden-variety jellyfish stings, which, if untreated, could potentially be fatal.

Myth #4: You Should Urinate on a Jellyfish Sting to Cure the Reaction

The idea that you should, well, pee on a jellyfish sting to reverse its effects is a remarkably pervasive one, and more than a few people learned the notion from a famous 1997 episode of the American sitcom Friends, of all places (“The One With the Jellyfish,” to be exact).

Well, don’t do it.

At best, urinating on a jellyfish sting does nothing for the pain or skin reaction, and just makes for a gross (and awkward) situation.

At worst, some evidence suggests it might actually exacerbate the reaction.

For many kinds of jellyfish stings, it appears the best ready-to-hand remedy is household vinegar, followed by application of heat or immersion in hot water.

Rinsing the sting site with vinegar for at least 30 seconds seems to neutralize the stinging cells.

(Lifeguards in jellyfish-prone areas typically keep vinegar among their arsenal.)

You’ll find conflicting reports with regard to vinegar’s effectiveness on the stings of the Portuguese man-o’-war, commonly called the bluebottle in Australia, where much research on jellyfish-sting treatments has been done. 

Some evidence suggests vinegar could worsen a bluebottle sting, and that rinsing with seawater and then applying heat or ice to the site is the better approach.

How best to treat the stings of particular kinds of jellyfish continues to be the subject of much research.

But we can say pretty definitively—at least based on current knowledge—that urination is not a worthwhile response, whatever Chandler did in that Friends episode.

Myth #5: Jellyfish Are Out to Sting You

The main reason why jellyfish are so well-armed with stinging cells has nothing to do with you.

Those nematocysts exist primarily to stun or kill the small prey—from zooplankton to baby fish—these cnidarians like to chow down on.

And while it appears that some sea jellies are more active hunters than others, many appear to follow a passive-feeding method of drifting with the currents and munching on whatever tiny organisms tangle with their trailing, stinging tentacles or oral arms.

When we’re stung by a sea jelly, it’s basically an accident: We’ve swum into one without realizing it, or currents drove a jellyfish into us.

Long story short: Jellyfish aren’t swimming around looking to sting people.

Myth #6: A Dead Jellyfish Can’t Sting You

Your average person may be more likely to see a jellyfish washed up on the beach than anywhere else.

Sometimes, in fact, large numbers of jellies (and those jelly-lookalikes by-the-wind sailors and bluebottles) wash ashore as beachwrack.

Many an overly curious beachgoer has discovered that dead jellyfish very much can still sting. The stinging cells can remain active for days or even weeks after the jelly exits this mortal coil, so best not to touch…

Some Surprising Facts About Sea Jellies

Now that we’ve sorted out some of the fiction surrounding jellyfish, how about a few jelly facts that verge on the unbelievable?

Jellyfish Composition

Here’s a startling fact, for one: Jellyfish don’t have a heart.

Indeed, they don’t have blood. Furthermore, they lack a brain.

We mentioned earlier that sea jellies are the simplest swimming organisms. They’re actually about 95 percent water.

They come suited up in three layers of tissue: an inner one (the gastrodermis), a middle one (the mesoglea layer), and an outer one (the epidermis).

Their main structure is a primitive digestive tract with only one opening for input and (ahem) output. Jellies respond to environmental stimuli with what scientists call a nerve net, spread throughout their body.

The Immortal Jellyfish

Certain kinds of sea jellies are among the very rare animals capable of shifting their lifecycle into reverse and essentially growing younger.

The most famous example is the aptly named immortal jellyfish (Turritopsis dohrnii), sometimes called the “Benjamin Button jellyfish” in reference to the famous story about a fellow who’s born an old man and then ages backwards into infancy.

If a free-swimming medusa form of the immortal jellyfish experiences some acute form of environmental stress or physical degradation, it can revert back into polyp form through transdifferentiation, in which one type of cell can turn into another type.

Scientists still don’t understand all the nuts-and-bolts of this reverse-aging process, which would seem to give an immortal jellyfish—unless it’s preyed upon or otherwise outright killed—the ability to essentially live forever.

Needless to say, however, there’s plenty of interest in the topic, given its potential implications for the human lifespan.

(And Turritopsis dorhnii isn’t the only jellyfish apparently capable of this miraculous feat; some form of it has been observed in certain other species, including moon jellies.)

The Giants of the Jellyfish World

Many sea jellies are pipsqueaks indeed—including such highly venomous pipsqueaks as those Irujandji box jellies, and that death-defying superstar the immortal jellyfish, which is about fingernail-sized.

But there are some true cnidarian hulks in the jellyfish family tree.

The lion’s mane jellyfish, widespread in the open ocean and often found in colder waters, may be the very largest.

A 19th-century report of a roughly 120-foot-long lion’s mane, if accurate, would make this species among the very longest animals known.

A lion’s mane relative, the Nomura’s jellyfish common in the Yellow and East China seas, is another contender, certainly when it comes to sheer mass: Specimens with a bell more than six feet across and a weight of some 440 pounds have been recorded.

Wrapping Up

Certain kinds of jellyfish (and jellyfish lookalikes) definitely warrant caution, given the severe stings they can deliver.

But that doesn’t mean we should mindlessly fear these spectacularly successful creatures, which have floated through the world’s oceans little-changed for some 500 or more million years.

Now doesn’t that deserve a little bit of respect?

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Hope this helps!