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Journey to the Microcosmos viewers will get a one-month free trial on Magellan TV by clicking the link in the description. The ciliates we’re going to talk about today are kind of frustrating.

At this point in our journey, we’ve gotten used to the fact that the microcosmos is an indecipherable mess at times, filled with organisms that look like each other, and who have familial relationships that seem obvious but then turn out to be a figment of our own limited imaginations. And these ciliates are yet another entry in the long-standing saga of ever-changing taxonomies that define our understanding of microbial species. The plot twist is inevitable.

We are going to be showing you these ciliates and talking about them like they are related, only to reveal at the end that they are not nearly as closely related as microbiologists once thought. But we still need to talk about these ciliates because, they are inescapable. They are always around, showing up in so many of our samples.

And we also need to talk about these ciliates because no matter how frustrating they are, they’re also a ton of fun to watch. These are a subclass of ciliates called hypotrichs. You might recognize that name because it’s shown up as a label on our channel before.

And perhaps you’ve wondered what exactly that means. “Hypotrich” sounds very cool, but it’s not really a super helpful label if you don’t know what a hypotrich actually is. And that is why we’re here today. But just so you know, it’s not a very specific label.

It does not tell us a whole lot about what species of organism we’re looking at. But sometimes, it’s the best we can do. After all, there are countless species of microbes in the world, many of which have names buried in books and papers we haven’t come across yet, and many others of which literally don't have names yet.

So for James, our master of microscopes, and—it should be said—a connoisseur of ciliates, labeling microbes sometimes becomes a matter of figuring out just how specific he can get. Sometimes, the best he can do is something broad, calling it something like “ciliate.” But sometimes there are details that help him narrow in a little closer. And hypotrichs have some pretty helpful details.

For one, they usually have a big mouth and a flat body. Some even have interesting pigments, like the gold dotting this frantically spiraling individual. Or this pink-tinted one.

Now we’re not sure what those pigments are or what purpose they serve, though based on what we’ve seen in other organisms, they could be a way to block harmful UV light from the sun. But things like a flat body or big mouth or pigments are not enough. What really sets hypotrichs apart from other ciliates is their thick hair.

Ciliates are hairy single-celled creatures, surrounded by thin fibrous organelles called cilia. And the arrangement of these cilia do so much to shape the way these organisms live, from the way the organisms move around the microcosmos to the food the cilia draw in towards the organism’s mouth. But even among ciliates, hypotrichs stand out for how they use their cilia.

They are not content to just have the thin structures their compatriots do. No, hypotrichs take these individual cilia and bundle them together into something bigger called a cirri, like a rope made of smaller strands. In some species, they may even have more than 100 cilia fused together in their cirri.

And it’s thanks to these cirri that hypotrichs do something unusual for single-celled organisms. They walk. You can really see it with this Aspidisca, which looks like it’s crawling across the screen like a little cartoon bug.

So the cirri help us know that we are looking at a hypotrich ciliate. But to narrow down the genus or species, we need to be able to see all of the cirri so we can make out the patterns they form along the hypotrich’s body. And it can be tough to see all of those cirri, which is often why we cannot identify our hypotrichs.

But there are some genuses that make it easier on us. For example, this stichotrich has a really distinct look to it thanks to its shape and the spiral of cirri traveling down it. And then there’s this diophrys, which has…well, it has a hairy butt.

And that makes it pretty easy to identify. It’s also very fast, we actually had to record this in slow motion to be able to show it to you. But this is also where things get confusing and complicated.

It’s where that plot twist comes in, the one we told you about in the beginning so it’s not really a plot twist anymore. It’s like watching The Empire Strikes Back for the fiftieth time when you know what’s coming, though I guess in this version, family bonds are getting broken instead of revealed. Because we’re talking about all of these organisms like they’re hypotrichs, except that it’s not clear whether that’s actually what they are.

And when we’ve been diving into the literature, the classifications get kind of confusing. What makes us feel a little better about ourselves is that it seems like the biologists find it a bit unfathomable as well. The 1979 edition of The Ciliated Protozoa described the taxonomy of hypotrichs as “aggravating.” It's good when scientists just tell it like it is.

Decades later, in 2021, a paper described them as “one of the most confused groups in terms of their systematics,” . It turns out that what defines an organism as a hypotrich or even a particular subclass of hypotrich depends so much on what you are reading. One of the more recent works dedicated to bringing more order to ciliate classification found that there were at least ten different taxonomic systems devised around categorizing hypotrichs.

And that’s how you get a story like the tale of the Euplotes. These ciliates were first described in 1733, and about 100 years later, the German microbiologist Christian Ehrenberg created the genus Euplotes around them. And they would end up being lumped in with many of the other hypotrichs as their own subclass, becoming one of the old guards of the hypotrichs.

Except, eventually, for taxonomic reasons, the Euplotes eventually became their own thing, separate from the hypotrichs but still related. The hypotrichs and euplotes simply became relatives, grouped together under a different family name: the spirotrichs. And on the one hand, this is the kind of thing that makes hypotrichs—and I guess, spirotrichs as well— so frustrating to talk about.

But it’s also something very cool. It’s like the microcosmos is a library that is constantly acquiring new books. And the more we read those books and add new ones to our shelves, the more we find ourselves needing to rearrange them so their location and neighbors reflect all that we have discovered.

Thank you for coming on this journey with us as we explore the unseen world that surrounds us. And thank you again to Magellan TV for sponsoring this episode of Journey to the Microcosmos. If you’re looking for some more microscopic content, make sure to check out Magellan TV’s “Life On

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The folks on your screen right now, they are the least frustrating thing in this video, I can tell you that. They are our Patreon patrons and they want it to be possible for us to continue banging our heads against books trying to figure out the relationships between hypotrichs. We'll figure it out someday.

But anyway, thank you so much to all of our Patreon patrons, if you would like to join them and be on of the reasons why we can make this show at all, that's Patreon.com/JourneyToMicro. If you want to see more from our Master of Microscopes, James Weiss, you can check out Jam & Germs on Instagram. And if you want to see more from us, there's always a subscribe button somewhere nearby.