PB&J, minus the PB, and completely different

Is immorality possible? Are jellyfish really fish or is “sea jelly” more accurate? Is one of the only truly immortal animals smaller than your pinkie fingernail? Did you know that sea jellies are brainless, heartless, and bloodless? What does a four point five millimeter long invertebrate eat? Do Immortal Jellyfish live forever because they can turn back into babies? Today with your host, Devon, and co-hosts, Chet and Cap, you will learn everything there is to know about the Immortal Jellyfish, Turritopsis dohrnii.

The riddle for the next episode is “Dear Valentine: Orchids are pink, insects like me are too, say your prayers, I might just eat you. Who am I?” You can send in your answers, questions, and episode suggestions to animals@kingdomanimaliapod.com and our website is at https://kingdomanimaliapod.com/kazpk.

Until next time, keep exploring this amazing Kingdom: Animalia.


Kingdom: Animalia - A Zoology Podcast for Kids is an animal podcast from Kingdom: Animalia Podcasts.

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Further Reading (Discovery of Immortality):

Read the Transcript for this Episode

[Devon] Hello and welcome to the fourth episode of Kingdom: Animalia - A Zoology Podcast for Kids. I’m your host, Devon, and these are my co-hosts,... [Chet] Chicka Chet... [Cap] ...Chicka and Cap! [Devon] Happy 2023 podcast listeners! Let’s hope this’ll be a good year. So let’s get this episode started. Today, on the first episode of Kingdom: Animalia - A Zoology Podcast for Kids in 2023, we’re talking about the Immortal Jellyfish, Turritopsis dohrnii; one of the world’s only biologically immortal animals. Enjoy fellow mortals.

[Devon] So far all of the animals we’ve talked about have had some things in common. A pair of eyes, two ears, an obvious mouth, lungs, A BRAIN... Today’s animal on the other hand (or the other tentacle), is very different. Immortal jellyfish have proportionally miniscule and simple– [Cap] Chicka Caps! [Devon] No Cap. Though it would look kinda cute if they wore caps... Nevermind. They have proportionally miniscule and simple eyes. They have no brain, no heart, no blood... I could go on. And the reason I said “proportionally” miniscule eyes is because... guess how big Immortal Jellyfish are. Are they A), four point five inches (or eleven point two five centimeters), B), four point five centimeters (or one point eight inches), or C), four point five millimeters (or zero point one eight inches) long? I’ll give you the answer, right after a quick break.

[Devon] Hello podcast listeners. Devon here, and I have some exciting news! We have a new contact email. Instead of kingdom.animalia.pod@gmail․com our email is now contact@kingdomanimaliapod.com. Don’t worry though, the old one still works {it has been since deleted. Do not email to it!! Use the new one!}. Again our new email is contact@kingdomanimaliapod.com.  And now back to Immortal Jellyfish.

[Devon] Welcome back to Kingdom: Animalia - A Zoology Podcast for Kids. I’m your host, Devon, and these are my co-hosts,... [Chet] ...Chicka Chet,... [Cap] ...Chicka and Cap! [Devon] Before the break I left you with a dangling question: are Immortal Jellyfish A), four point five inches (or eleven point two five centimeters), B), four point five centimeters (or one point eight inches), or C), four point five millimeters (or zero point one eight inches) long? [Chet] Chicka A! [Cap] Chicka A! Give me a drumroll please, Chet... [Chet] Chicka Coming right Chicka up! [Devon] The answer is... C! One of the number one longest living animals is... only four point five millimeters or zero point one eight inches long and with a bell (that's the dome part of a jelly) diameter of four point five to ten point one six millimeters or zero point one eight to zero point four inches. They have transparent bells and along their rim grow up to NINETY tentacles, but individuals that live in tropical waters — like around Panama — have less tentacles, around eight, while jellies in more temperate waters have twenty-four or more. Younger individuals are one point zero one millimeters or zero point zero four inches long and have eight tentacles. Their tentacles are white, and their transparent bell allows you to see their bright, red stomach. Like most jellies they have what’s called a hydrostatic skeleton, which is simply a cavity inside of the jelly that is filled with water, called a mesoglea. You may have noticed that when referring to “jellyfish” I’ve been saying “jellies”, so I’ll explain. There are many sea creatures called “fish” such as cuttlefish; shellfish; starfish; and, of course, jellyfish. None of those organisms I mentioned are actually fish and unfortunately some do not have more accurate names, but some do. The new and more accurate term for “starfish” is “sea star” and similarly the more accurate term for “jellyfish” is “sea jelly”.

[Devon] Moving on... Immortal Jellyfish buy caps in two ways: at stores and online. [Cap] Chicka I know Chicka you’re just Chicka trying to Chicka trick me. [Devon] You got me Cap. Immortal Jellyfish feed in two ways: passively and actively. They forage passively mainly as immatures by hanging out on the ocean floor and chowing down on any little food bits that float their way. They actively hunt by swimming around in the ocean and stinging their prey with their tentacles. Their diet is mainly plankton, fish eggs, animal larvae, and brine shrimp (a kind of tiny crustacean which isn’t truly a shrimp).

[Devon] Now let’s talk about how they have more Immortal Jellyfish. They can reproduce both with a mate (sexually) — when they’re in their mature life stage, the medusa — and by themselves (asexually). They reproduce as adults with a partner similar to their namesake, fish, by spawning; where the baby Immortal Jellyfish develops outside of the mother’s body. They reproduce without a partner through a cloning process called budding, in which the jelly breaks off into multiple individuals; I’ll talk more about that soon. [Cap] Chicka I wish Chicka I could Chicka clone caps.

[Devon] Okay, since the riddle, the intro, and of course me saying their name, you’ve probably been wondering how an animal could possibly be immortal. So let’s do a crash course on Immortal Jellyfish Immortality. [Cap] Chicka Part one: Chicka Life Cycle.

[Cap] Chicka Life stage Chicka number one: [Devon] An egg. The Immortal Jellyfish first starts off as a fertilized egg floating in the water.

[Cap] Chicka Life stage Chicka number two: [Devon] The planula. After a few days the egg turns into a larva called a planula. They’re microscopic and look almost like a worm that can swim around freely.

[Cap] Chicka Life stage Chicka number three Chicka A): [Devon] The polyp. The planula then swims to the ocean floor in search of a solid surface, such as a seabed or a rock, to attach themself to. This polyp stage is when they develop their digestive system.

[Cap] Chicka Life stage Chicka number three Chicka B): [Devon] Preparing to bud. When the water conditions are right for them they start to elongate and segment their body into a small,

linked colony of young jellies that looks almost like a stack of pancakes. [Chet] Chicka I prefer Chicka birdseed.

[Cap] Chicka Life stage Chicka number four: [Devon] The ephyra. After developing new muscles and nerves a segment of the polyp pancake stack breaks off and becomes an independently growing, feeding, and swimming ephyra. In this stage they start to look more like an adult sea jelly.

[Cap] Chicka Life stage Chicka number five: [Devon] The medusa. The medusa is normally the final stage of a jelly’s life. In this stage they are fully mature and can have babies with another jelly. Most jellies would then die after spawning, but...

[Cap] Chicka Part two: Chicka Immortality.

[Cap] Chicka Step number Chicka one: [Devon] The cyst. So say an Immortal Jellyfish finds themself in a life threatening situation; they may be starving, injured, too cold, too hot, or just getting old. Their fate appears to be sealed, but then the jelly does something miraculous. They sink to the sea floor once more and transform into a tiny blob called a cyst.

[Cap] Chicka Step number Chicka two: [Devon] The polyp. [Chet] Chicka Devon, you Chicka already did Chicka the polyp. [Devon] Yes I did; but this is how they escape death. They turn back the clock. Once they’ve become a cyst they then transform back into a polyp.

[Cap] Chicka Step number Chicka three: [Devon] Weaknesses. Though this ability can save them from many threats, there’s a reason it’s called “biological immortality” and not just “immortality”. Turning back into a kid can’t save them from predation, disease, poisoning (for them that would mainly be caused by water pollution), and having a persistent lack of food. If they’re not exposed to predation, disease, water pollution, and food shortages they could theoretically live forever.

This concludes our crash course on Immortal Jellyfish Immortality

[Devon] This incredible feat of immortality is hard to believe. It’s then hard to imagine that it was discovered... completely by accident! [Chet] Chicka Whaa...? [Cap] Chicka Whaat...? [Devon] It was. Many scientific discoveries have been made by accident. And one of them... was immortality. Now I’m going to tell you the story of how an unsuspecting biology student stumbled upon one of the greatest feats of nature. It all started in the summer of 1988. German marine-biology student, Christian Sommer, was spending the summer— [Chet] Chicka Sommer was Chicka spending the Chicka summer? [Devon] —...in Rapallo, Italy. Sommer was researching hydrozoans, which are small marine invertebrates. Each morning of his stay he would go snorkeling in the water off the cliffs of Portofino. While snorkeling, Sommer would collect any hydrozoans he could find using plankton nets. Among the hydrozoans he collected was a tiny, four point five millimeter long, unassuming hydrozoan known only at the time as Turritopsis dohrnii. Sommer would keep the hydrozoans he found in petri dishes to observe their behavior. Several days after their capture Sommer noticed that the T. dohrnii specimens he had collected were acting strangely — in a way he could not explain. Once in their medusa form, when they should die, they would seem to age backwards. They would get younger and younger until they were back at the beginning of their cycle, and just start over. Sommer was confused by this occurrence, but he didn’t know how significant it was. T. dohrnii wouldn’t be dubbed “immortal” for almost ten years. Sommer didn’t proceed to continue research on these strange invertebrates, but several biologists became very interested in his findings. They then continued to study the species and then eight years later, in 1996, these scientists published a paper on T. dohrnii called “Reversing the Life Cycle.” The scientists explained how this bizarre species could — at any life stage — turn back into a polyp. So that’s how the Immortal Jellyfish’s immortality was discovered. How’d you like the story Chet and Cap? [Chet] Chicka There was Chicka no popseed Chicka to eat Chicka during it.

[Devon] Now... of course... it’s time... for predators. [Chet] Chicka Uh, oh... [Devon] Immortal Jellyfish are preyed upon by Sea Anemones, larger sea jellies, Tuna, Sea Turtles, Penguins, and Swordfish. That’s it. We made it through.

[Devon] Now we’re going to talk about where they live. [Cap] Chicka Devon? [Devon] Yes? [Cap] Chicka Can I Chicka do it Chicka this time? [Devon] Y’know what, I think you can. Here’s the script Cap. [Cap] Chicka Okay. Chicka eh-eh- Chicka -hem. Chicka It is Chicka thought that Chicka Immortal Jellyfish Chicka originated from Chicka the Mediterranean Chicka Sea, though Chicka now they Chicka are found Chicka in oceans Chicka around the Chicka world. Chicka This invasion Chicka of the Chicka Immortal Jellyfish Chicka has mostly Chicka been caused Chicka by humans. Chicka This is predominantly Chicka because these Chicka sneaky sea Chicka jellies are Chicka hitching rides Chicka on boats. [Devon] Why thank you, Cap. [Cap] Chicka You are Chicka very welcome.

[Devon] Now, who’s ready for some FUN FACTS?!? [Chet] Chicka I am! [Cap] Chicka I am!

[Chet] Chicka Fact number Chicka one: [Devon] Despite Immortal Jellyfish’s small size —four point five millimeters or zero point one eight inches long— they can swim at up to four point nine miles or seven point nine kilometers per hour! That’s four hundred and ninety-three point seven body lengths per second, which is unbelievable. Other sources said six point nine miles or eleven point one kilometers, but that seemed too crazy, so I decided to go with the quote on quote “low” estimate.

[Chet] Chicka Fact number Chicka two: [Devon] They are the only sea jelly that doesn’t stay in their medusa stage until they die.

[Chet] Chicka Fact number Chicka three: [Devon] If they starve or get sick as a polyp, they can’t regenerate, and they’ll die.

[Chet] Chicka Fact number Chicka four: [Devon] They are not a true sea jelly. True sea jellies belong to a scientific class called Scyphozoa, while Immortal Jellyfish belong to the class Hydrozoa, as mentioned in the story.

[Chet] Chicka Fact number Chicka five: [Devon] As mentioned in the beginning of the episode, sea jellies have no brain! They also don’t have blood or a heart.

[Chet] Chicka Fact number Chicka six: [Devon] Sea jellies are almost completely made up of water! To be specific they’re ninety percent water! That’s why if you ever see a dead sea jelly washed on the beach they’re an unrecognizable blob, since they’re out of the water.

[Devon] Now let’s do the Glossary where I’ll explain some words from the show you, and especially younger listeners, may not know.

Word number one: Passive or passively. To do something passively is to do it with very little effort.

Word number two: Plankton. Plankton are any super small, typically microscopic, organisms that float around in the ocean. Some plankton are just animal larvae, who will grow out of being plankton, but others are plankton their entire lives.

Word number three: A scientific class. In this context a scientific class isn’t what you’d think it would be. It’s a level of classification. The levels of classification group together more and more related organisms, all the way down to one specific organism. The levels go: Kingdom, Phylum, Class, Order, Family, Genus, Species. Species is the lowest you can go. Like, for instance, human, is a species.

[Devon] We’ve reached the end of episode four! I can’t believe we’re here. This show has come so far. Next episode will be a milestone: number five! Another thing that’s exciting about this episode is that it’s the first one, other than the trailer and The Songs of Sparrows, to be published in real time — once I’ve finished recording it! [Chet] Chicka This is Chicka exciting. [Devon] Yeah. So as usual, if you want to know where I got my information, or learn more about Immortal Jellyfish, you can look at my works cited page which is linked in the show notes and is on the page for this episode at: kingdomanimaliapod.com/episodes/immortaljellyfish. The episode comic is linked there, in the show notes, and the url is kingdomanimaliapod.com/comics/immortaljellyfish. You can contact me at my email which is contact@kingdomanimaliapod.com or use the contact page on my website which is at kingdomanimaliapod.com/contact. You can use these to send me questions, episode suggestions, and your guesses for the riddle for the next episode. So here it is: “Dear Valentine: Orchids are pink, insects like me are too, say your prayers, I might just eat you. Who am I?”. So, any guesses? Send them in, and I’ll tell you if you got it right, but if you get it wrong you’ll have to wait until February to find out. So, until next time, enjoy your time as an ephyra or polyp, and keep exploring this amazing Kingdom:, Animalia. Bye! [Cap] Chicka Bye! [Chet] Chicka Bye!

[Cap] Chicka Three,... two,... Chicka one... Chicka Happy Cap Chicka Year!

Check the Works Cited for this Episode

Message from Devon:

Happy 2023, podcast listeners! 🎉 🎈


Cap (Co-host)
a year ago

Chicka The year Chicka of the Chicka Cap!

Devon (Webmaster)
a year ago

Year of the rabbit, actually.

Cap (Co-host)
a year ago

@Devon (Webowner) Chicka Agree to Chicka disagree!!

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