There’s no such thing as a jellyfish
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There’s no such thing as a jellyfish


Everyone is familiar with the basic idea of
a jellyfish, but what do we mean when we use that term? The most commonly seen are things like sea
nettles, which can bother swimmers and be stranded ashore as amorphous brown blobs. These are some members of the Scyphozoans. Their life cycles typically include a polyp
stage, attached to the bottom, which produces baby medusae. When conditions are right, these babies can
grow up to form vast blooms of adult jellies. But for every moon jelly, pulsing in coastal
waters, pYthere are deep-sea relatives which defy generalizations — they can be a meter
across, 20 meters long, and lack tentacles. The branch of the tree of life called Scyphozoa
also includes another lineage: the Coronate medusae. Typically found in the deep sea,
they can be brightly bioluminescent and many lack a polyp stage in their life cycle. All of these scyphozoans are Cnidarians (the
C is silent), relatives of sea anemones and corals. This group is defined in part based
on the presence of stinging cells. The most infamous stingers are the sometimes
lethal box jellies, found in tropical waters, but most Cnidarians pose no danger to humans. Most species of swimming jellies are actually
in another group called the Hydromedusae. These are often small and transparent. They
may have very few tentacles…. Or very many. They might or might not have a small polyp
stage called a hydroid. One group of hydromedusae has tentacles which
point ahead of them instead of trailing behind. These eat other gelatinous organisms, rather
than the crustaceans favored by many other Cnidarians. But even with all this diversity we haven’t
yet encountered the most unusual Hydrozoans. Would you consider a siphonophore a jellyfish?
From the Portuguese man-o-war floating on the surface,
to dozens of species found in the deep sea, these are among the strangest of marine animals.
They have divided up the tasks of living among different subunits. Some parts pulse to move
the animal through the water, but can’t feed. Others, connected by a thin tube that runs
the length of the body, can feed, or reproduce, but not swim. Although siphonophores can grow to be 30 meters
long, the most common are small (rocket-shaped) species, found throughout the ocean. Those are the Cnidarians, including some of
the most familiar and unfamiliar animals that might be called jellyfish. They all have in
common the presence of stinging cells called cnidae. Not all jellies sting, though. Another deep
branch in the tree of life leads to the Ctenophores, also known as comb jellies. Their defining trait is 8 rows of ciliary
plates, which flutter like eyelashes to move them through the water. Some species use sticky
tentacles to capture prey, much like a spider web. Others lack tentacles, but use tooth-like
cilia in the mouths to bite and swallow gelatinous prey.
Many deep-sea species are so fragile that they are new to science, or have only been
described since the advent of submarines. Nearly all are bioluminescent, and many have
red or black pigmentation which is thought to mask the bioluminescence of ingested prey. The next group that is often lumped with jellyfish
are the Urochordates, including salps, doliolids, and larvaceans. These are the most vertebrate-like
of invertebrates, with many traits shared with chordates.
Salps are typically colonial, forming units that can be tens of meters long. Each unit
within the colony pumps water through their body, filtering out phytoplankton and even
smaller particles. As such, they are the jellyfish that subsist directly on plant material.
Because they grow and reproduce rapidly, salps and doliolids can form dense blooms in many
regions. Larvaceans are relatives of salps which, during
development, do not change their body form from their tadpole-like larval stage. Larvaceans
filter particles using a mucus house that they secrete and inflate, sometimes many times
each day. The mesh is so fine that they are able to retain and ingest even bacteria-sized
particles. So the factors that lead to changes in salp
populations, and the effects that salps have on ocean ecosystems, are very different from
the causes and effects of changes in Cnidarian and ctenophore populations. We know of slugs and snails that crawl on
the ground, but a variety of molluscs live in the water column, flapping their feet to
swim. Many have even retained their shells, although typically in a reduced form. Many kinds of worms also live a gelatinous
life. This includes polychaetes (distant relatives of earthworms). One of the most abundant deep-sea
animals below 2500 meters depth is a polychaete with fans of long setae — the bristles that
characterize polychaetes. Other segmented worms,- transparent and beautifully
bioluminescent lack these bristles, and swim around preying on gelatinous organisms.
Some worms, with two beady red eyes, are parasites and predators on jellies. So is there really such a thing as a “jellyfish”.
Are they only circular Cnidarians or also elongated ones? Do they sting people or eat
microscopic plants? Are they rare and elusive, or poised to take over the world? All across
the tree of life, organisms have evolved jelly-like adaptations, and each has its own way of thriving
and surviving. Understanding their diversity is an important first step to understanding
life in the largest habitat on earth. this is Steve Haddock from the Monterey Bay
Aquarium Research Institute. If you see any jellyfish-like creatures, be
sure to report them at jellywatch.org�

100 thoughts on “There’s no such thing as a jellyfish

  1. @Simpsonsfreak1134 : your statement is a little too simplistic. *Phylogenetically* speaking salmon are more closely related to camels than to hagfish, but that doesn't mean that they "have more in common" if you acknowledge that salmon and hagfish have many ancestral traits in common that dominate their phenotypes. The camel is a highly derived vertebrate form relative to either "fish." Those derived characters result in it having much less in common biologically than do salmon and hagfish.

  2. @podwel This is YouTube, of course it needs to be simplistic. The point is that we call nearly everything that swims a fish and they have biologically nothing to do with each other. I find this fascinating and so did Stephen Jay Gould.

  3. The video is brilliant! Thanks very much for such detailed information. However, the subtle tone of the narrator's voice and meditative music are making things a bit sleepy at the end.

  4. I especially appreciate the nomenclature assistance via the graphics. This is a really nicely thought out and informative video.

    Thanks for this YouTube channel and and for Jellywatch!

    PS. Please consider regularly transcribing your YouTube videos for the hearing impaired.

  5. We're happy to hear that you enjoyed and learned from our video. Also, thank you for the suggestion about transcribing our videos for the hearing impaired. We've added captioning to this video and will do so for all of our future YouTube videos.

  6. Excellent stuff. I'm gathering some reference photos of these things, to study them as training for visionary art. The names help a lot. Fantastic source of inspiration, thanks for uploading.

  7. The Narcomedusae are the jellies whose tentacles point ahead of them instead of pointing behind like most jellies. The little yellow one in the video with 4 tentacles pointing ahead is called Aegina citrea.

  8. hey many sea jellies eat adult fish and even other jellies! did you forget about the group of jellies called cubazoans? did you forget that people in Asia eat sea jellies, salp jellies are in the same group as humans, and many jellies reside in freshwater lakes and rivers!

  9. Hello, I loved the video. The question I have had for ever is how do the jellys produce that pulsating rhythmic movement? I imagine it is not a nerve impulse to muscle cell activation mechinism, so what is it?

  10. A jellyfish has a ring of muscle around its bell. When a jellyfish tightens this muscle, its bell closes. This pushes water inside the jellyfish out, shooting the jellyfish forward. As the muscle relaxes, water refills the bell. This is how they pulse in the water. Each tentacle can be moved by its own muscles, as can the oral arms. Jellies have a nerve ring that connects the rhopalia (sensing organs) and a nerve net that can send messages around the bell to contract and release.

  11. Cool , so there is a connection through the nerve ring from sensing organs to oral arms , bell and tentacles, without the need of a brain allowing the jelly to respond to environmental stimuli ?

  12. I thought the common red and blue coloration was because those colors "disappear" in various deep levels of water because of the frequency of the light waves.

  13. well then, there's no such thing as a bird, snake, whale, or shark, either… from what I've seen, you've just been calling jellyfish by their scientific names, and saying "They aren't jellyfish!"

  14. A cnidarian scam is where a jellyfish emails you claiming to be a distressed diver in an attempt to lure gullible people into the water for a snack.

  15. Terrific video man. I always thought the same. It always seemed to me the term "jellyfish" was just lazily thrown out there for the meantime, while these gelatinous-like organisms from every branch of life were truly and more accurately classified.

  16. I  love this channel but this was one of the best videos. I really hope to see more in this style. It was very educational and interesting to watch. I love learning the names of these animals and where they fit in the tree of life, GREAT video. Thanks!!

  17. Does anybody know what the species of hydromedusae is at 1:34? I was thinking it was a nacromedusae but a came up with nothing if anybody knows the specific species that would be appreciated.  

  18. There is such a thing as a jellyfish. It's the medusa stage of any Cnidarian. Everything else is gelatinous zooplankton or sea jellies, but not necessarily jellyfish.

    Folk taxonomy does not have to follow the same rules as scientific taxonomy. Jellyfish can be a polyphyletic grouping and still be valid in people's conception of life.

    As long as people realise it's a cultural term, and not something based in our current scientific classification system, I don't think there's a problem using "jellyfish".

  19. From each ecosystem they devour, a new brother will rise and be made whole. Their numbers will grow and they will live forever.

  20. Sorry but jellyfish is a valid terminology. It's the standard vernacular applied to free moving members of Medusozoa.
    https://en.wikipedia.org/wiki/Jellyfish

  21. There is no such thing as a fish either, at least if one wants to include lungfish but exclude mammals, yet the term "fish" is such a useful term that I doubt anyone but the most ardent cladists are going to care much that people use it 😉

  22. Thank you for this wonderful video. I have not heard this vocabulary pronounced since college. Back in the day we rarely had such good video to augment the text books.

  23. then what r they then. Blobs that no one cares about? Well, jellyfish are called jellyfish for a reason. They just have different names. And if you say, there are no jellyfish, then they would not exist :/ this makes no sense.

  24. i feel like god is just up there somewhere puffing on a cigarette and being like: "humans?? nah. over it. but JELLYFISH?? now THATS where its at!!"

  25. You may wany to rename my, our beautiful jellyfish but they will always be jellyfish to me, us. Cheers from the barrier islands!

  26. The comments here are mostly missing the point. They say "well, if there are no jellyfish, then what are they?" The video is not here to say they don't exist – the video is only here to say that "jellyfish" is not a taxonomic term. A classic sea nettle, for example, is a jellyfish, but closely-related corals are never called that, while Comb Jellies are sometimes called jellyfish.
    You see? The term "jellyfish" is not very helpful as a taxonomic description. It would be better to call some of them "medusae", others "comb jellies", and so forth, as the term is mostly just aesthetically descriptive.
    Shoutout to @moara for actually making an educated definition and defence of the term (unlike most of the commenters).

  27. One of the facts that I found to be interesting while learning biology in college is that some "jelly fish" can essentially be eternal. Going from the polyp stage back to the medusa stage. Medusa stage back to the polyp stage..

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