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SOURCES:
https://pubmed.ncbi.nlm.nih.gov/18795820/
https://www.britannica.com/science/protozoan/Mechanisms-of-food-ingestion
https://www.microscopyu.com/gallery-images/peranema-protozoan-videos
https://www.micrographia.com/specbiol/protis/flagell/flag0100.htm
This episode was sponsored by Wren,  a website where you calculate your   carbon emissions.

You can also sign  up to make a monthly contribution to   offset your emissions or support  rainforest protection projects. Tardigrades are famous for their capacity  to survive.

If you look them up, you will   be inundated with long lists of the many things  scientists have thrown their way to see if the   tardigrade will survive. We’ve made some lists  like those ourselves. Tardigrades on the moon,   tardigrades in extreme heat.

You’ve heard about  them. We’ve talked about them. What else is there?  Well, here’s a surprising fact you might not  have known.

For certain species of tardigrades,   like the one in the middle  of your screen right now,   you can tell the difference between a male  and a female by looking at their toes.  That’s right. The toes. These tardigrades are called Milnesium,   and the males of these species have a pair of  claws on their feet that are shaped a little bit   differently from the rest of the claws, with only  one hook on each claw instead of the usual two.   But after taking a closer peek  at this tardigrade’s toes,   we can confirm that she is a female tardigrade.

Now, that’s a fun fact for us as we watch   the clip. But it does not actually do  anything for the poor rotifers that are   surrounding this tardigrade, who are currently  stretching themselves in and out of danger.  Around the tip of a tardigrade’s mouth are small  bumps that we think act like little sensors.   And when those bumps make contact with a rotifer,  out pops the tardigrade’s stylet—a needle that   pokes out from the tubular mouth opening. That stylet pokes into the rotifer,   and from there the tardigrade uses a circular  structure called a pharynx in its head   to create strong suction.

And then, the stylet  goes from functioning as a needle to functioning   as a portable, built-in straw that lets the  tardigrade suck out the inside of its prey.  You can see some of the bodily fluid leaving  the rotifer as the tardigrade’s stylet pumps   away like a beating heart. And when she is done,  the rotifer remains, like an empty coffee cup.  This method of eating works quite well for  the tardigrade, letting her eat quickly from   the prey that is directly in front of her.  But not all organisms come equipped with a   weapon that lets them turn rotifers into Capri  Suns. These organisms have to turn to other   methods to extract nutrients from their food.

This marine ciliate is called kentrophyllum, and   it came to James, our master of microscopes, in  a large container full of beach sand. On a normal   day, maybe we would talk more about its funny  almond shape that stretches as it swims around.  But today is not a normal day  because this kentrophyllum is   about to be overshadowed by a rotifer. Now, where is the rotifer, you might ask?  It is inside the kentrophyllum, of course.  We did not catch the moment of its capture,   when the toxic needles lining the kentrophyllum  darted out and paralyzed the rotifer.

By the   time we arrived, the rotifer had already  been ingested…but it was not dead yet.  You can see it wiggling and wrestling  at the broad end of the kentrophyllum,   causing the ciliate’s body to wrinkle and  fold in on itself. But it is trapped inside   of a food vacuole now, a compartment  that exists to break this rotifer down.  Sure, the rotifer can try and fight  against the walls of the vacuole holding   it hostage. But there’s not much it can do  against the digestive enzymes pouring in,   or the increasing acidity of its surroundings.  A food vacuole is a hostile place to be, and for   minutes, its destructive tools will go to work.

In the end, the rotifer will be left in dissolved   pieces to be absorbed by the kentrophyllum’s  cytoplasm, sustaining the organism that   was the site of its last battle. It’s a lonely death for the rotifer,   with only the kentrophyllum to witness it.  Though I suppose now there is also us, sharing   and immortalizing that rotifer’s last moments. And if the rotifer had not died in the body   of another organism, it may have  ended up like this gastrotrich.  Now to be fair, they did find themselves in  a very similar situation: they are both dead.  But the rotifer was eaten alive, digested from  the outside while trapped in another organism.  Meanwhile, this gastrotrich is going through the  exact opposite situation.

It is being eaten from   the inside out, by a scavenger called a peranema. Now, as far as we know, the peranema didn’t do   anything to kill the gastrotrich. It was likely  already dead, though we don’t know what killed it.  But the peranema is both a hunter and a scavenger.  Sometimes it can be found with other peranema as   they hunt down prey, in a pack of hungry microbes.

At other times, the peranema scavenges. They   are notorious for being able to  squeeze their way into whatever   holes they find to get into a dead organism. And in this case, the gastrotrich’s exoskeleton   was the right combination of available, open,  and dead for the peranema, which found its way   in and decided to begin helping itself to the  buffet of dead tissue around it.

After all, the   gastrotrich won’t be needing that tissue anymore,  so the peranema might as well make good use of it.  The gastrotrich’s body has likely vanished  by now. Perhaps the peranema will have   finished it off entirely, or some other  scavenger will have joined in on the fun.  Or perhaps, it will have simply faded,  like the rotifer inside the kentrophyllum,   its body eventually fading into  the world that encapsulates it.  But for this last moment, let’s remember  the gastrotrich in a more beautiful moment   under a fluorescent light, glowing in the  glorious purple autofluorescence of its remains.  Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.  And thank you again to Wren for sponsoring  this episode of Journey to the Microcosmos. Wren is a website where you can  calculate your carbon emissions,   then offset them by funding projects like  community tree planting in East Africa   or a project that uses satellite monitoring and  drones to detect and prevent deforestation in the   Amazon rainforest.

We will need a lot of different  approaches to take on the climate crisis,   and this is one way that you can learn more about  your carbon contribution and take some action. You’ll answer a few questions about your  lifestyle and they’ll also show you ways   you can start reducing your carbon emissions.  No one can reduce their footprint to zero,   but when using Wren, you can  offset what you have left. Once you sign up, you’ll receive  updates from the tree planting,   rainforest protection, and  other projects you support.

And we’ve partnered with Wren  to protect an extra 10 acres   of rainforest for the first 100 people who  sign up using our link in the description! There’s a group of people in the world, and  their names are on the screen right now,   who really rather like chill videos about  tardigrades sucking the insides out of rotifers.   They are our Patrons on Patreon. They’re the kind  of people who think to themselves, “You know,   I would really like for this kind of content to  exist and so, they give us a little bit of money   every month so that we can keep doing it.

And we  really, definitely, could not do it without them. If you would like to become one of those people,  you can do that at patreon.com/journeytomicro. And if you’d like to see more from  our Master of Microscopes James Weiss,   you can check out Jam & Germs  on Instagram or on TikTok.

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