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Imagine that this is the beginning of the last thing you’ll ever see, an empty landscape with thin lines scratched across it. But those lines suddenly sharpen and gather into a dense mass that spreads from the crown that sits atop a giant, studded with greens and yellows. A giant that is in search of one thing: food.

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SOURCES:
https://www.microscopyu.com/gallery-images/collotheca-rotifera
https://ucmp.berkeley.edu/phyla/rotifera/rotifera.html
http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/rotidr.html
https://web.deu.edu.tr/atiksu/ana55/other1.html
https://www.nationalgeographic.com/science/article/bdelloid-rotifers-80-million-years-without-sex
https://www.tandfonline.com/doi/abs/10.1080/10236244.2017.1344554
https://www.gbif.org/species/1000703
https://www.researchgate.net/profile/Sss-Sarma/publication/340493224_Observations_on_the_egg_types_and_males_of_Collotheca_tenuilobata_Anderson_Rotifera_Collothecidae/links/5e8d043ba6fdcca789fde0b7/Observations-on-the-egg-types-and-males-of-Collotheca-tenuilobata-Anderson-Rotifera-Collothecidae.pdf

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Imagine that this is the beginning of the last thing you’ll ever see, an empty landscape with thin lines scratched across it.

But those lines suddenly sharpen and gather into a dense mass that spreads from the crown that sits atop a giant, studded with greens and yellows. A giant that is in search of one thing: food.

And then imagine, that you are that food. Tiny in the face of this alien whose body is designed to take you in and break you down. And as it retracts, pulling away from the scenery, you disappear with it.

We're letting magnification and music do a lot of the heavy lifting when it comes to setting the scene. Up close, this animal is upsetting, its movements slow until they are sudden, peaceful until they are predatory. But from further away, things are a little different.

It still looks strange, but it seems less overwhelming than before. It seems just kind of chill, even as this other large organism brushes by. The animal we’ve been focused on belongs to the genus Collotheca, making it one of our favorite types of animals: a rotifer.

And we’ve happened upon many rotifer mishaps and adventures in the microcosmos before. They’re always being bullied or eaten or caught up in some tragic tale of their own making. But in the case of the Collotheca, their biggest bullies might be themselves.

Because these organisms love to eat, even if that means eating each other. Collotheca are put in an awkward position when it comes to seeking out food because they can’t easily hunt it down. Most Collotheca species are sessile, which means they don’t really swim around.

Instead, they spend most of their lives stuck, attaching themselves to whatever is in their vicinity and seems like it might be a good home, like the ones you see here. And while they’re there, the Collotheca surround themselves in a gelatinous tube, giving them a sort of squishy sleeping bag they can retract into when something disturbs them. And it turns out, it’s very easy to disturb them.

Those long threads we saw at the beginning of the video aren’t just decoration. They are there to help the rotifer sense the world around them, both so they can recognize danger and so that they can find food. The hairs are called cilia, and we’ve seen them on other rotifers before.

In fact, they’re a defining feature, part of the inspiration for the name “rotifer,” which translates to “wheel bearer”. It’s the fast spinning whirling motion of the cilia that gives the head of the rotifer its wheel-y appearance. But while the cilia are notable on all rotifer, they are particularly long and noticeable on the Collotheca.

And they also seem to be extremely sensitive. James, our master of microscopes, has found that if he’s recording Collotheca, he has to be extra careful to not walk around the microscope. If he does walk, the vibrations in his steps reach the Collotheca and drive them to retract into their gelatinous safety vest.

Like other rotifers, Collotheca appear to be able to use their cilia to create currents that draw food into their mouths. Whether it’s algae or some other kind of single-celled organism, or even a tiny crustacean like a water flea, the Collotheca probably doesn’t care as long as it gets fed. It uses its enormous mouth to close in on whatever it’s eating, wrapping it up in the bony jaw called the trophi, and then swallowing its prey in a jerky motion.

Based on what James has observed, he’s been starting to suspect something kind of funny about how Collotheca get their food because sometimes, you’ll see smaller organisms just swim right into their mouths. So James thinks they may be getting a little extra help, that when the Collotheca retracts into itself, it’s actually pushing a little bit of the stuff in its stomach into its giant mouth. And in that regurgitated mass are nutrients that could be attracting single-celled organisms toward the rotifer.

Now we’re not sure if that’s what happening—that the rotifer is puking into own mouth to lure in more food. But if it is true, it's still not the weirdest way that Collotheca gets a meal. That would probably be the cannibalism.

But not just any form of cannibalism will do for the Collotheca. It is specifically, a baby cannibal, fully willing to eat its own child. Cannibalism is a striking behavior for Collotheca, but not necessarily a surprising one.

In the same study where this behavior was documented, another non-Collotheca rotifer was observed engaging in sexual cannibalism, where the female rotifer would eat the male rotifer after mating was completed. That behavior is not unheard of in the animal kingdom, where insects and spiders turn their last mate into their next meal. It’s not clear if Collotheca do the same thing to their male counterparts.

In fact, for a long time, it wasn’t even clear that they had male counterparts. We’ve known about Collotheca for more than a century, but the first male Collotheca wasn’t observed until 1986. And it turns out that male Collotheca were generally smaller, and most importantly, their lifespans were super short—on the order of 20 hours.

It is as if they were born just to breed and then die soon after. But we're getting away from our original topic: the cannibalism. The captions from the paper documenting this tell the story quite succinctly.

From Panel

A: “female neonate emerging from gelatinous tube.” From Panels B-

D: “adult female ingesting female neonate.” It’s simple, poignant, and tragic for the female neonate. It’s also completely unclear to us how common this behavior is, and why the rotifer mother might engage in it. It does not seem to be a great way to pass on your genes. Perhaps it was just in need of a nutritious snack, perhaps it was a mistake.

Perhaps, in the microcosmos, rotifers can't be choosers. Thank you for coming on this journey with us as we explore the unseen world that surrounds us. And thank you especially to these people here on the screen right now, they are our patrons on Patreon.

They make it possible for us to continue to explore this bizarre and beautiful world, and to make observations that we can't yet confirm but hopefully some day we will be able to. Like that rotifers, maybe, puke in their own mouths to attract food. If you like what we do here you can go to Patreon.com/JournytoMicro.

If you want to see more from our master of microscopes, James Weiss, you can check out Jam & Germs on Instagram or TikTok. And if you want to see more from us here, there's always a subscribe button somewhere nearby.