YouTube: https://youtube.com/watch?v=llel7yCxUKc
Previous: What Do These Algae Do With Four Genomes?
Next: The History of Red Algae

Categories

Statistics

View count:124,251
Likes:4,015
Comments:240
Duration:44:48
Uploaded:2023-11-27
Last sync:2024-02-09 09:30
We have a complicated relationship with worms. On the one hand, they’re gross. They end up in body parts and cause disease. On the other hand, they’re everywhere. You cannot escape worms, especially in the microcosmos.

Follow Journey to the Microcosmos:
Twitter: https://twitter.com/journeytomicro
Facebook: https://www.facebook.com/JourneyToMicro

Shop The Microcosmos:
https://www.microcosmos.store

Support the Microcosmos:
http://www.patreon.com/journeytomicro

More from Jam’s Germs:
Instagram: https://www.instagram.com/jam_and_germs
YouTube: https://www.youtube.com/channel/UCn4UedbiTeN96izf-CxEPbg

Hosted by Hank Green:
Twitter: https://twitter.com/hankgreen
YouTube: https://www.youtube.com/vlogbrothers

Music by Andrew Huang:
https://www.youtube.com/andrewhuang

Journey to the Microcosmos is a Complexly production.
Find out more at https://www.complexly.com

Stock video from:
https://upload.wikimedia.org/wikipedia/commons/b/bc/Nathan_Cobb_Nematologist.JPG
https://upload.wikimedia.org/wikipedia/commons/thumb/4/4c/PSM_V87_D075_G_B_Grassi.png/466px-PSM_V87_D075_G_B_Grassi.png
https://www.nasa.gov/images/content/545578main_nemotodes_lg.jpg
https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Images/iss042e155226.jpg
https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Images/iss042e136581.jpg

SOURCES:
https://ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html
https://blogs.scientificamerican.com/artful-amoeba/parasitic-roundworms-own-this-place/
https://www.britannica.com/animal/annelid/Classification
https://animaldiversity.org/accounts/Annelida/
https://sciencing.com/earthworm-closed-circulatory-system-6787995.html
https://www.microscopemaster.com/phylum-annelida.html
https://arstechnica.com/science/2022/04/army-of-worm-larvae-hatch-from-mans-bum-visibly-slither-under-his-skin/
https://www.healthline.com/health/worms-in-humans#symptoms-of-infection
https://link.springer.com/book/10.1007/978-1-4020-8239-9
https://www.frontiersin.org/articles/10.3389/fmicb.2021.689987/full
https://link.springer.com/article/10.1007/s13127-020-00469-6
https://www.nature.com/articles/s41598-018-36396-y
https://www.backyardnature.net/n/a/aeolosom.htm
https://www.smithsonianmag.com/science-nature/14-fun-facts-about-marine-bristle-worms-180955773/
https://ia800708.us.archive.org/view_archive.php?archive=/22/items/crossref-pre-1909-scholarly-works/10.1002%252Fjmor.1050160204.zip&file=10.1002%252Fjmor.1050170202.pdf
https://keys.lucidcentral.org/keys/v3/TFI/start%20key/key/Annelida%20key/Media/Html/Aeolosomatidae.html
https://www.journals.uchicago.edu/doi/abs/10.2307/1538737
https://manoa.hawaii.edu/exploringourfluidearth/biological/invertebrates/worms-phyla-platyhelmintes-nematoda-and-annelida
https://www2.gwu.edu/~darwin/BiSc151/Coelom/Coelom.html
https://www.mun.ca/biology/scarr/Coelom_formation.html
https://ucmp.berkeley.edu/platyhelminthes/platyhelminthes.html
https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/41%3A_Osmotic_Regulation_and_the_Excretory_System/41.3%3A_Excretion_Systems/41.3B%3A_Flame_Cells_of_Planaria_and_Nephridia_of_Worms
https://sciencing.com/flatworms-roundworms-reproduce-10021662.html
http://www.nhc.ed.ac.uk/index.php?page=24.25.333.369
https://ucmp.berkeley.edu/annelida/polyintro.html
https://animaldiversity.org/accounts/Polychaeta/
http://plymsea.ac.uk/id/eprint/373/1/NotesontheecologyofCirratulus(Audouinia)tentaculatus(Montagu)..pdf(http://plymsea.ac.uk/id/eprint/373/1/NotesontheecologyofCirratulus%28Audouinia%29tentaculatus%28Montagu%29..pdf)
http://www.seawater.no/fauna/annelida/cirratus.html
http://www.thecephalopodpage.org/MarineInvertebrateZoology/Eupolymniacrassicornis.html
https://www.smithsonianmag.com/science-nature/14-fun-facts-about-marine-bristle-worms-180955773/
https://ucmp.berkeley.edu/annelida/polymm.html
http://www.nhc.ed.ac.uk/index.php?page=24.25.333.369
https://www.nature.com/articles/s41586-019-1418-6
https://news.byu.edu/there-are-57-billion-tiny-wormlike-nematodes-for-every-human-on-earth-now-we-know-where-most-of-them-live
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC126866/
https://ohioline.osu.edu/factsheet/plpath-gen-8
https://www.thoughtco.com/nematoda-free-living-parasitic-roundworms-4123864
https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2014/07/free-living-nematodes-as-indicators-of-biological-soil-health
https://elifesciences.org/articles/05849
https://www.ncbi.nlm.nih.gov/books/NBK20086/
https://www.yourgenome.org/facts/why-use-the-worm-in-research
https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=1032
Here on Journey to the Microcosmos, we have a complicated relationship with worms.

On the one hand, they are gross. They wiggle around.

They end up in body parts. They cause disease. All those things aren't great.

On the other hand, they’re everywhere. You cannot escape worms, especially in the microcosmos. And given everything we have said about how gross worms are, that doesn’t sound like good news.

But there’s something to be said for ubiquity. Absence may make the heart grow fonder, but constant worm encounters can go a long way too. We might even have a little affection for them at this point.

So today, we’re going to look back on some of those many encounters and see what it is that makes worms so hard to ignore. Let’s start out though by talking about what a worm actually even is. There are no ghosts in the microcosmos.

There is no Halloween in the microcosmos. But if there were, this flatworm would fit in quite nicely with its spectral appearance. It might be navigating its way through a field of other organisms, but it looks like it had three minutes to prepare for a costume party and decided to go with the classic “old bedsheet with eyeholes” ghost costume.

And maybe comparing this flatworm (or even worms in general) to a ghost is kind of apt. Ghosts straddle two worlds, and so do worms, though in their case, instead of bridging the realm of the living and dead, worms manage to stretch between the micro and the macro. This creature you’re watching now would probably be difficult to see without a microscope.

But on the other end, there are worms that are meters too long to observe with a microscope. And akin to ghosts, worms might seem like a sort of reduced form of life. After all, for a lot of us, worms are the wiggly tubes that we dug up from playgrounds.

And of all of the worms, flatworms are perhaps the most simple of all. But even digging into what it means to be the simplest worm makes the whole notion of simplicity seem ludicrous. So let’s start with the broader question: what are worms, other than wiggly, self-mating tubes?

While we generally use the word “worm” to describe many different, unrelated, invertebrate, tubular animals that belong to a number of different phyla, there are three main phyla that people focus on. The first are our flatworm buddies here, who are known more formally as Platyhelminthes. Then there is the phylum Nematoda, known less formally as roundworms.

We’ve come across nematodes many times in our journey through the microcosmos, which makes sense given that they are one of the most abundant animals on this planet. And last are the Annelida, phylum of our playground friend, the earthworm. While earthworms are a bit beyond the scope of the micro, if you will, we’ve also got this little Stylaria lacustris.

At the tip of its head is the proboscis, an antenna-like structure that the worm uses for feeding. And as we scan past the head, you can see that the length of the Stylaria’s body is segmented. Of the three phyla we’ve mentioned, annelids are the most complex.

They have a closed circulatory system with tubes that transport nutrients and oxygen throughout their body, as well as a complete digestive system that has both a mouth to take in food and an anus to get rid of waste. If we think of worms in general as a gut enclosed within a body wall, then that gut is a tube and the body is a tube, and you can imagine that worms are a tube inside a tube. Now what separates these different groups is the space that separates one of those tubes from the other.

Complex systems inside annelids are due to what’s called a coelom, a tissue-lined cavity that sits between the tube of the digestive tract and the tube of the body wall. Importantly, this cavity is filled with fluid, which facilitates the development of organs along with the transport of nutrients around the body. The development of the first coelom was a very big deal because coeloms don’t just allow annelids to have complex systems.

They connect the seemingly simple organisms we’re talking about here to more complex animals—like us! Because annelids and humans are both what is known as coelomates, or eucoelomates. We are animals that have coeloms.

So, thank you to the ancestor that we share with earthworms who developed the first coelom, who allowed more complex organisms like you to exist. Nematodes, on the other hand, are what are called pseudocoelomates. They still have a coelom-like fluid-filled cavity, but the cavity isn’t lined with tissue like you find in true coeloms.

Other microscopic pseudocoelomates include gastrotrichs and rotifers. This pseudocoelom is a slight but significant difference in nematodes when compared to annelids, corresponding to a slightly less complex body plan, though nematodes still do have a complete digestive system. The flatworms are the simplest of all.

Starting with the coelom: flatworms don’t actually have one. They’re considered acoelomates. That area between the gut and body wall where annelids and nematodes have a cavity full of fluid is instead full of tissue.

This has a few consequences for the flatworm, but one of the biggest ones is that this area can’t support the development of specialized systems that you see in other animals. The lack of coelom imposes limits on the flatworm’s body and lifestyle, reducing both its complexity and size. But that does not mean the flatworm lives a simple life.

Of the three worm groups, flatworms are the most like a tube within another tube, except that their outer tube is much less cylindrical. The “flat” in “flatworm” is actually an adaptation: without a circulatory system or respiratory system, the worm relies on diffusion across its outer membrane to supply cells with oxygen. Being flatter gets the cells closer to the outside and better positioned for diffusion.

And without the ability to build a complete digestive system like those found in nematodes and annelids, flatworms have to adjust to life without that most under-appreciated body part of all: the anus. They take in food through one opening, digest it in their gut, and then spew the waste back out from that same opening. So unlike other organisms who have separate entrances and exits for their food, the flatworm must wait to finish digesting before it can eat again.

But this is not the only way flatworms can get rid of waste. Their body is lined with a special type of cell called a flame cell that also gets waste out of the worm. While it may not have the elegance of an interconnected set of organs, this system is its own form of complexity.

Basically, every flame cell is one single-celled kidney, allowing the worm to just...ooze waste from its skin. And this is just scratching the surface of the biological intricacy flatworms are capable of. Like many of their more involved worm counterparts, flatworms can reproduce both asexually and sexually.

And when reproducing sexually, they can mate with another flatworm, or even with themselves--both making and fertilizing their own eggs. There’s also those flatworm species that can regenerate, a trick that our more developed bodies are, alas, not capable of. Even the many weird ways they move make the word “wiggle” feel reductive.

Our perception of simplicity across nature is built on comparisons. Compared to us, an earthworm may seem simple. Put that earthworm next to a flatworm, and suddenly the earthworm represents a gigantic biological advancement.

But then put that flatworm next to a bacteria, and suddenly it contains multitudes, it is a universe. That flatworm is a marvel, an almost unbelievable testament to the power of evolution. So we started with the simplest worm of all.

And if you’re someone who is skeptical that worms can be interesting, then maybe watching a simple, jiggly tube was not enough to sway you. But nature has a way of building on simplicity, creating fascinating creatures out of even the most basic of blueprints. And that brings us to the next worm we’re going to focus on… the ones we affectionately call “polka-dotted vacuum worms.” We recently did an episode about nematodes, the phylum of worm that outnumbers just about every animal on this planet.

Now, it's not the most striking of animals, but the nematode has had a few distinguished scientific decades, thanks to its many uses in laboratories. So as far as worms go, the nematode seems to dominate much of our scientific understanding. But worms, despite their seemingly simple bodies, are a diverse bunch.

Which is why we thought for today it might be fun to visit with a less famous worm and like one of those relatives that you don't really know very much about But every time you see them, there's a new strange story to unpack They are the Aeolosomatids, a family of freshwater worms. The ones that you see here are invaders. They showed up uninvited in a blepharisma culture that James, our master of microscopes, has been taken care of for a long time.

And while Aeolosoma worms are you know, worms, they are in a different class of worm because as we have seen before, there are, in fact, many ways to be a tube. Where nematodes are roundworms, Aeolosoma are segmented, placing them in the Annelid phylum, along with earthworms and leeches, Aeolosoma are usually several millimeters in length, their bodies divided into more than ten segments that you can see scrunching up and expanding as the worm wiggles its way through the microcosmos. The Aeolosoma are striking to look at.

You can see their organs through their transparent bodies, and as it moves, bundles of long bristly hairs wave along the side of its body. Those hairs mark the Aeolosoma as a specific type of an annelid called a polychaete, or bristle worm. Some bristle worms are found in unusual places like hydrothermal vents, but our Aeolosoma come from a much more mundane home.

They're usually found in bodies of fresh water where they'd like to crawl among the leaves and algae that settle at the bottom of the water. And inside their bodies are colorful gland cells, though no one is really sure what those cells exist for or why they have their particular colors. And some species, the cells are green and others they're yellow.

And sometimes, as with our worms, they're red. The final result is a worm that looks a little like it ran into a porcupine while also having caught chicken pox. While there are some Aeolosoma species that reproduce sexually, most reproduce asexually dividing to form a copy of itself.

The Aeolosoma creates its clone at its end, linking the old and new versions of itself like a chain. You can see the new Aeolosoma here, looking like it's attached to the other’s butt because, it's attached to the other’s butt. And this chain can keep going as the Aeolosoma keeps dividing, adding more worms that are connected together so that the final length of their combined bodies sometimes reaches around ten millimeters total.

That's ten millimeters of clones combined to create one giant mega worm until eventually the chain breaks and they all go their separate ways. So when James found these worms invading his samples, you'd think maybe this would be an exciting find. Here is a culture full of bristled, polka-dotted, chain-forming clones.

What could be more exciting! Well, as wonderful as they are to look at these invasions are not ideal because they are also essentially vacuum cleaners. Their mouths are lined with cilia that wave around and help the worms suction up bits of plant and animal debris.

When they're in a pond, They like to crawl across leaves and algae for their meals. But when you find them in bottles of ciliate cultures, you've been lovingly maintaining, that's when things get a bit dicier. Because Aeolosoma will eat just about anything, including each other.

Indeed. in one very dramatic scene documented in 1901 scientists observing the species Aeolosoma tenebrarum described the way these chains of worms would twist up in each other, creating a writhing, tangled ball of worms that would stay stuck together for long periods of time. And when the scientists pulled these balls apart, they usually found at least one worm that had been partially eaten. I'm sure the etiquette around cannibalistic frenzies varies, but for most animals, getting eaten by another member of your species would seem, at the very least, a little rude.

But when you're Aeolosoma, it's not that big of a deal. Honestly, it's not much more than an inconvenience, because if a part of it gets eaten, it can always regenerate. In one case, the scientists watching these balls of worms found that one worm had its head eaten.

But in about three days it was able to make a new one. It would probably have taken less time to regenerate other parts of their body- heads seemed to take the Aeolosoma a bit longer, perhaps because of all the complex parts that need to be rebuilt. And the Aeolosoma can regenerate even when it is cut into multiple segments.

This superpower has made one species called Aeolosoma viride particularly interesting to scientists. And it's not just that they can regenerate. After all, as incredible as this ability is, there are plenty of other animals that can regenerate as well.

But scientists aren't just interested in how animals regenerate. They also want to know how those regenerative abilities change as the animal gets older. That's a difficult question to study because as you might expect, self-healing animals have often, pretty long lifespans.

So it's a challenge to wait years or even decades to study how their ability to regenerate changes with the wear and tear of aging. Aeolosoma viride however, has a lifespan of only about two months, which means it goes from young to old on a manageable timescale for scientists cycling through experiments. And that makes it a useful organism to observe how that capacity to rebuild itself changes as the worm ages.

But as useful as regeneration is for survival, it is not the only tool the worm relies on. After all, not all dangers can easily be patched up by rebuilding body parts. Sometimes the worm has to preempt dangerous conditions, and for that it turns to the cyst.

In nature, the worms will likely begin forming these cysts in autumn, when the water gets cold and begins to fill with the remains of decomposing life. And as the temperatures continue to fall, the worms begin to slow down, crawling to areas full of delicious debris for them to stock up on, and eventually, the worms begin to secrete a mucus, creating a gooey shell that then hardens into a cyst. You can see the granules of red pigment swirling around as the worm moves inside.

Some of that activity might be the peristaltic movement of its intestines, but it's also possible that the warmth of the microscope lamp is causing the worms to stir as well. And in their ponds, when warm weather comes, the worm will get ready to emerge from its encased hibernation, using its head to push at the hardened case of its cyst until it manages to poke a hole through from which it can escape. It can take a worm anywhere from 30 minutes to several hours to make its exit.

And if there's a thick coating of bacteria on the cyst, it may even take the worms several days. And from there well, it is a life of suction, feeding and chain link clones and regenerating. Perhaps not normal to us, but what's normal anyway?

Especially when you're a worm. Now that we’ve seen a few worms, have you ever wondered what it would be like to live inside of one? Because I certainly haven’t.

But there is a ciliate that does like to live in the guts of worms, so in our next video, we’re going to learn more about why they do that. You’ve heard some worm horror stories, right? We were looking some up just for this episode and came across a recent headline from ArsTechnica that read, “Army of worm larvae hatch from man’s bum, visibly slither under his skin,”.

And if that’s not enough to terrify you, and make you feel very uncomfortable there’s always the stories of painful stomach cramps or diarrhea or nausea that eventually turns out to be caused by some worms that have taken up residence in someone’s intestines. It is terrifying and wild to think of something so much smaller than us causing so much havoc. So, as we watch the cilia lining a worm’s gut beat its own soothing pattern, wouldn’t it feel like, almost like, a little bit of justice if this sight wasn’t so peaceful?

If worms had to worry about their own guts being taken over by a parasite? If you’ve found yourself in this position, seeking schadenfreude over a worm, well we have some good news for you. The worm you see in the middle of this tank is currently hosting this strange fellow, called a Radiophyra.

James, our master of microscopes, had been on the hunt for the Radiophyra after seeing this: two radiophyras linked together in a chain as one divided to make more copies of itself. It had come from the inside of one of the worms he’d been watching, when he’d accidentally squeezed a worm a bit too hard under the coverslip and caused the ciliate to pop out. Radiophyra belong to a general group of ciliates called Astomes, or astomatid ciliates.

We’ve talked about ciliates a lot on our channel, which means that if you’ve been watching us for a while, you may have picked up on the fact that from time to time, we have said that most ciliates have an oral groove, that opening lined with cilia that sweep bacteria and algae and other tiny bits of food into the organism. We’ve seen that oral groove at work in ciliates like stentors and paramecium, functioning as the ciliate equivalent of a mouth. But as we have always said most ciliates, you will have inferred, that this does not mean all ciliates.

And if you are looking for an exception to the rule, astomes are that exception. Astomatid ciliates are diverse, but they are unified by one shared feature, or rather, they are unified by their lack of one shared feature, a mouth. And they don’t need a mouth because they have something even better.

They have worms. Astomatid ciliates do parasitize animals other than worms. Some live inside mollusks, others inside leeches or even in amphibians.

But they are most commonly associated with the guts of annelid worms. So when James found his Radiophyra, he decided to see if he could find more of them in the other worms that were in his samples. And that meant that our master of microscopes had to become a master of worm surgery, dissecting them so he could draw out the ciliates living within.

In–side this particular aquatic worm were these astomatid ciliates. From a distance, they also look like worms. But as you get closer… And closer, their shape becomes more definite except for the massive amounts of fluff around them, a dense cloud of cilia beating away.

Unfortunately, there isn’t a lot of research on this ciliate. In fact, there isn’t a lot of research on astomatid ciliates in general. They just aren’t destructive enough or common enough to have become either a necessary or convenient research subject.

In fact, it’s not even clear whether or not we should call them parasites. Modern day papers will sometimes refer to them endosymbionts instead, because we don't know a lot about whether astomatid ciliates are doing much to their worm hosts, bad or good. But the worm gut does plenty for the astomatid ciliates.

At one point in time, the ancestors of these ciliates did have mouths. But as they found their way into worms, and specifically their guts, those oral grooves became less and less necessary. Instead, the ciliates could rely on a form of feeding called osmotrophy, where they simply absorb nutrients from their surroundings through osmosis.

Instead of taking in larger bits of food through their mouths and breaking it down themselves, astomatid ciliates could just take advantage of the worm’s digestive system to do all that breaking down for them. As the worm’s digestive enzymes break down complex molecules into simpler forms  that can travel through their own intestinal walls, some of those nutrients would just go feed the astomatid ciliate instead. These ciliates will actually sometimes be picky about making sure they’re in a particular spot within their host’s intestinal tract.

And once they’ve found the right spot, the ciliates hold themselves in place with organelles that range in shape, some use hooks, other spines, or maybe even suckers. The flat shape of the ciliates helps them stay pressed to the epithelium of the intestines. So while these ciliates may not need a mouth anymore, they have found other traits necessary to their survival.

Astomatid ciliates are found in hosts from all sorts of environments. Some live in soil. Some live in ponds.

Some even live in ocean waters. And scientists are using the general tools available now to try and piece together how host and endosymbiont have shaped each other. We can see some of that intertwined story in the ciliate’s mouthless-ness, but the specifics of that evolutionary change are laid out in their DNA, as are the other more hidden parts of that shared history.

Now we cannot know whether worms have any feelings about their guts being home to another organism. They likely don’t have much choice in the matter, and they also likely aren’t prone to emotions like resentment the way we might resent a worm parasitizing our bodies. But if they were to have any feelings on the matter, we want to offer this one last detail about astomatid ciliates: many of them have their own endosymbionts as well, bacteria that live inside them with perhaps their own history tangled up with their ciliate host’s story as well.

Now we couldn’t find those bacteria in our parasitic friends, but we like the idea that somewhere out there are these nesting dolls of endosymbiosis: an organism that is an organism but an organism that is also a home buried within other homes. When we say that worms are everywhere, we mean it. Even in the world of science, worms are widespread with researchers turning to the nematode Caenorhabditis elegans as a model to study all sorts of questions.

And in the process, scientists have written some lovely things about the nematodes that make their work possible. So in our next video, we’ll pay tribute to a worm that has shaped our world in so many ways. When it comes to the muses of the animal kingdom, the nematode seems like an unlikely well of inspiration.

There may be poems about tigers burning bright, and epic fantasy tales featuring giant birds. But nematodes have two obvious factors working against them achieving that kind of mythical status.

First: they are worms. And let's not generalize too broadly, but their simple tubular bodies are just not what most people think of when it comes to the beauty of the natural world.

Second: most of them are really tiny, their length measured in millimeters. It’s hard to be inspired by an animal that is likely to escape one’s notice entirely. Though we should note that there are nematodes that can grow quite long—the largest discovered was found in the placenta of a sperm whale, and it measured between 8-9 meters in length. But even that seems more likely to inspire more nightmares than art.

In 1914, a scientist named Nathan Cobb wrote the following about nematodes: Nematodes do not furnish hides, horns, tallow, or wool. They are not fit for food, they do not produce anything fit to eat; neither do they sing or amuse us in any way; nor are they ornamental —in fact, when they are displayed in museums the public votes them hideous. Judging from that quote, Cobb seems to understand the common consensus on nematodes, which is that if there is to be a consensus, it is not a positive one.

But Cobb wrote this as part of a 34 page paper on nematodes titled “Nematodes and their Relationships,” which wonderfully documents his fascination with the worm and argues for their importance to our understanding of the world. So clearly, he found something inspiring about the nematode. But there is another quote from this research paper that you may have even heard before, it is pretty famous in nematode circles.

And The quote is as follows: In short, if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes. Cobb paints a world overrun by nematodes, an image created by his own experience with studying them. But when he wrote this, he likely didn’t have the means to estimate just how many nematodes there are in the world.

But in 2019, researchers estimated that there are about 57 billion nematodes in the world for every human in the world. In addition, their total biomass is about 300 million tons. And that’s just for the soil nematodes.

When you take into consideration nematodes living in freshwater or marine habitats or inside of other animals, the numbers only go up from there. Nematodes are considered to be one of the most abundant animals on earth. But the beauty of Cobb’s writing on their abundance is that he doesn’t just capture the notion of the numbers.

The world he describes isn’t just a mass of worms that we’ve been allowed space inside of. The world he describes—the one that we live in—has its forms and landscapes sculpted and cultivated by worms, their bodies shaped around and inside trees and plants and animals. Of course, not all of those links between nematodes and other organisms are always so pleasant.

In “Nematodes and their Relationships,” Cobb mentions that he once removed over 40,000 nematodes from the stomach of a wallaby. And if that isn’t daunting enough to imagine, there are always the ancient texts that date back thousands of years, documenting intestinal worms found in people. There are also the nematode eggs that have been found preserved in mummies and in fossilized poop.

In the 19th century, scientists were able to show that the parasite Ascaris lumbricoides which resides in the intestines and produces eggs that are passed on through poop finds its way into people who have ingested their eggs on contaminated food. To prove this, a scientist named Giovanni Battista Grassi infected himself with their eggs and then hunted for those eggs in his feces. A peculiar aside here this is not the first time we’ve described a scientist hunting through his own poop for evidence of the microcosmos you can watch our Leeuwenhoek episode for more tales of this type.

Now there are plenty of other nematode parasites that have their own unique life cycles and horrifying effects. Some worms are transmitted through the soil, others through insects. Some inflame the limbs, others trigger massive blood loss.

Nematodes can also parasitize plants, attacking the roots or stem or flowers, sometimes destroying entire crops in the process. And so with such a destructive path, the nematode feels like an enemy, something we study only to understand how we can fight it. But Cobb asks a simple question in his writing: What would be our conception of the insect group as a whole if our knowledge was largely confined to these simple and degenerate parasitic forms?

In the case of insects, we have enough experience with them to know that whatever squeamishness they inspire, they are also integral parts of our world. And likewise most nematodes are actually free-living species. It’s just that the parasites have come to dominate both our imagination and our knowledge because of their proximity and their consequences for our health.

But those massively abundant soil nematodes they are vital to our world, feeding on bacteria and fungi. In the process, they release nitrogen back into the soil, sustaining other organisms and plants that may use it. A healthy soil is full of these free-living nematodes, whose presence reflects the overall diversity of microbes around them.

The information is all there, it is up to us to uncover their secrets. Perhaps this why Cobb ended “Nematodes and their relationships” with this call to arms for the field of nematology: They offer an exceptional field of study; and probably constitute among the last great organic group worthy of a separate branch of biological science comparable with entomology— nematology. We can’t speak to any claims that the nematode is the quote “last great organic group” worthy of its own branch of study.

But we do feel that he has been vindicated by the fact that one of the most popular model organisms used today is a free-living nematode: Caenorhabditis elegans, better known as C. elegans. While the worm is found in soils all over the world, what it’s perhaps best known for is the life it lives in labs. While scientists had described various aspects of C. elegans life early in the 20th century, it wasn’t until 1965 that the scientist Sydney Brenner turned to the worm as a model organism, relying on its fast life cycle, small size, and capability to produce more than 1,000 eggs a day.

There were those who thought the worm’s simplicity would render it useless in studies of morphology and behavior. But time and technology has turned C. elegans into a molecular muse. It has taught us about how life develops, how human diseases progress, and how cells die.

When Cobb wrote, “My experience in this matter makes me very confident in saying that professors of biology could do far worse than to introduce into their courses a more careful examination of these creatures,” he didn’t know that one day, many of those professors of biology wouldn’t just be introducing nematodes into their courses. They would be introducing them into their labs. When Cobb died in 1932, scientists didn’t even know how genetic information was encoded in DNA.

More than 50 years later, C. elegans became the first multicellular organism to have its genome sequenced. And as it continues to teach us about our world, NASA has even sent them to space so we can learn about how life ages outside of this planet. So maybe the nematode is not the muse we expected.

But over the past century, they’ve become one nonetheless. And perhaps that is the most fitting testament to what a muse often actually is, a surprising source of inspiration that seems to come from nowhere, and then permeates until you see it everywhere. We’ve been on a journey in this compilation through knowledge and a growing appreciation for worms.

And it brings us to our last video, where we went from not just being resigned to the presence of worms, but actively seeking one out and dealing with all the surprising challenges along the way. We have spent most of our journey through the microcosmos seeking out the organisms that are too small to see with the human eye. The bacteria, the ciliates, the tardigrades.

And Part of what makes them so exciting to find is that they are so tiny. Every moment we spend with one of these organisms is a peek into something exceptional in our experience of the world, and it’s the result of how much work James, our master of microscopes, has to put into hunting down as many microbes as he can. And sometimes, that effort requires a lot of persistence.

Take the creature we’re going to focus on today: the bristle worm. This has been one of the white whales for our channel for some time. And as you watch it, you can perhaps understand why we have been searching so hard for it.

It’s got the body of a pipe cleaner with the head of a cartoon dragon. And maybe you also understand that just because we’ve been wanting to find one of these worms, that doesn’t mean we are guaranteed anything. After all, one of the things you have to accept about the microcosmos, and microbe hunting, is that it is a big world full of tiny creatures, and it can take a while to find some of them.

The fact that we are showing you one of those bristle worms right now spoils the twist we would usually build into, but, surprise, we found a bristle worm! The real twist is that this was not the first bristleworm we found. This was the first bristle worm we found.

Twenty centimeters of segments and bristles climbing up the side of a tank before burrowing back beneath the sand. Unfortunately, that’s just about all the video we got of that bristle worm. James spent so much time trying to find this bristle worm again that he started to feel a connection to it.

So he decided to give it a name: Gunther. James spent hours trying to catch it without hurting the worm. But Gunther has hundreds of appendages that can grab onto sand, and James didn’t want to accidentally snap the worm in half with his tweezers.

So instead of showing all the features of Gunther that we wanted to show, we’re going to show clips of this bristle worm instead because it kind of resembles Gunther, except a lot tinier. Gunther is hopefully still somewhere in that tank, living a nice life in the burrow it dug for itself. But it’s hard to know exactly where in the tank Gunther made its home because it would only show activity in the dark.

The moment James tried to turn the lights on and watch the worm in motion, it would vanish again under the sand. And as it became harder and harder to find, James kept hoping that one day, something would bring another bristle worm to him. And then, one day, James received a package from a coral farm containing sediments and other things that might contain some interesting organisms.

We talked about some of those organisms that James found in our last episode. But in addition to all of those organisms, James found several species of his long sought after bristle worm. Bristle worms are also known as polychaetes, and they’re part of the segmented worm phylum known as Annelids.

The name “polychaete” translates in Greek to “many hairs.” Those stiff hairs are called setae, and for most polychaetes, they’re attached to paddle-like appendages called the parapodia that branch off each segment of the worm. Our giant friend Gunther most likely belongs to the order Eunicida, but its microscopic look-alike is more unknown to us. But we can imagine that it spends its life crawling around the sand and feeding on algae, or whatever else it can take a bite out of.

You can see this one moving its mouth in slow motion, like a weird pair of pincers inside clamping down on something, and the movement is even more dramatic in full speed. This probably looks like a bunch of tiny individual orange worms tangled together. But it is, in fact, a worm belonging to the genus Cirratulus that can get to around 12 centimeters in length.

And along with its distinctive color, the worm is easy to spot in wet sandy mud because of those threads you see waving across your screen. Some of these threads are tentacles, but others are actually gills. And in the water, those threads seem to float serenely.

But this effect is lost on land. In a paper from the beginning of the 20th century titled “Notes on the Ecology of Cirratulus tentaculatus,” the author wrote, “When withdrawn from the mud Cirratulus presents an exceeding limp and bedraggled appearance.” This worm has a more imposing appearance but also a funnier name. It belongs to the terebellid order, but it’s known as a spaghetti worm.

These tropical worms live in sand, building tubes out of gravel and limestone to live in. Their tentacles spill out from the tube, sometimes extending as far as a meter to gather building materials and food for the worm. To reproduce, spaghetti worms will release their eggs and sperm into the water, but only at night and sometimes even without other males or females around.

They seem to do this on a lunar cycle, with a limited two week window for these gametes to release and find each other. That seems like an extraordinarily chance-y way to reproduce, but it seems to work for this worm. These are the bristle worms we were able to find from our coral farm samples.

And so it seems like our hunt for this white whale might be over. Except, the more we’ve been reading about bristle worms, the more we wish we could find even more. Because these are an animal whose existence seems designed to inspire lists of fun facts and bizarre trivia.

There are thousands of species of polychaetes, and they all seem to have something remarkable or weird about them. Some spend their lives in tubes that stick up from the sand, using their parapodia to paddle water through the burrow. Others have managed to carve out lives near hydrothermal vents.

Some sound like they’re straight out of a horror novel, growing up to ten feet long or dining on the bones of decomposing animals. And some even have eyes on both ends of their bodies. So knowing that all of these different species are out there, how could we ever end our quest for the bristle worm?

Thank you for coming on this journey with us as we explore the unseen world that surrounds us. The people whose names are on your screen right now, they are our Patreon patrons. Thank you so much to all of them, and if you want to become a patron you can go to Patreon.com/JounreytoMicro.

If you want to see more from our master of microscopes, James Weiss, and why wouldn’t you, check out Jam & Germs on Instagram, and if you want to see more from us, there is always a subscribe button somewhere nearby.