This episode is sponsored by Surfshark.

Get  Surfshark VPN at surfshark.deals/microcosmos   and enter promo code microcosmos for an  83% discount and 3 extra months for free.  Rotifers don’t really get a lot of love  when it comes to microscopic animals.   At least as far as the public imagination goes,   the rotifer is overshadowed by its fellow  metazoan of the microcosmos: the tardigrade.  And we might be part of the problem. In the first  few months of the channel, we did spend an entire   episode on our rotifer friends.

But despite  how often they show up in our videos, spinning   their wheels, we have many more videos focused on  tardigrades…and we even made a tardigrade T-shirt.  Of course, there is a very simple explanation  for this. Tardigrades are weird-looking,   but they’re also kind of cute. At times,  they may even seem kind of cuddly.  Rotifers, on the other hand…well, they’re mostly  just weird.

Very cool, but also very weird.  But rotifers are making a bit of a comeback—a very  literal one. This year, researchers announced that   they were able to recover a living rotifer  frozen inside 24,000 year old permafrost   collected from a river in northeastern Siberia. While some species of rotifers have been noted   for their tardigrade-like ability to withstand  long periods of low temperatures, scientists had   previously observed those periods to be more on  the order of 6 to 10 years.

That’s still a pretty   impressive amount of time to survive freezing  conditions, but it’s a far cry from 24,000 years.  This doesn’t mean that we should be expecting  ancient rotifers to be popping out of the   ground or anything. It’s just that it’s  so remarkable to imagine a world where   tardigrades aren’t alone in their complex bodies  and resilient capabilities…and then to realize   that world isn’t imaginary. That rotifers have  been right there alongside them the whole time.  And so today, we want to take a moment  to appreciate the rotifer from the inside   out.

With many animals, that would require  dissection. But fortunately for us,   a little bit of strong light and our most  recent microscope updates lets us see the   inner machinations of the rotifer at work. It’s almost like we’re on a field trip,   huddled together on some kind of magic school  bus as we journey through the organism itself.   All around us is a living exhibit  made up of around 1,000 cells.  That number of cells will stay constant  over the course of the rotifer’s lifetime.   But there are also about 2,400  known species of rotifers,   which means there have been at least 2,400 ideas  of just how to put 1,000 cells to good use.  So what we’ll be seeing today are just some  of those uses.

Because it turns out, there   are many many many different ways to actually be  a rotifer and to actually look like a rotifer.  But different as they may be, there are  a few traits that unite these strange   swimming organisms—including what  will be the first stop on our tour.  This is the corona, the moving,  hairy crown atop the rotifer   that gives it the name “wheel bearer.” It will  look different for different species, but this   spinning headband shares one specific purpose: to  stir up the water and bring food to the rotifer.  Then the food will pass on to  another part shared by all rotifers:   their jaw, also called the trophi, which  is settled into a muscular structure   called the mastax. You can see it at work here,  opening and closing inside the rotifer’s head   as it passes food from the  head to the rest of its body.  Jaws have evolved many times in the animal  kingdom over the past 500 million years or so,   which means that you can find a lot of  different jaws out there in the wild.   Even among rotifers, there are at least 9  different types of trophi that we know of,   and their shape depends on  the diet of the rotifer.  And as you look around at the trophi, what  you’re seeing is an engineering marvel.   There are at least seven distinct parts to  it, each with their own set of actions that   they perform over the rotifer’s lifetime without  wearing down or breaking. They grab, they crush,   they pierce.

It’s like a tiny little  machine inside the rotifer, which is why   researchers have even looked to the trophi  as inspiration for future tiny little robots.  Does that mean we can expect a rotifer  robot any time soon? Probably not.   But who needs robots when we’ve got the  real live thing right here in front of us?  The trophi’s main purpose is to pass food from  the outside to the inside, which takes us to our   next—and perhaps most perilous—stop, the stomach,  with its enzymes designed to break down food.  Though…if the rotifer is male, you might not  actually have to watch out after all because   there might not be a stomach...because they  just don’t live long enough to need one.  Rotifer species differ in how they approach the  necessity of males. There are some that have   done away with the concept of males entirely,  relying on asexual reproduction to survive.  Others will keep them around for a short time,  though primarily for sexual reproduction.   These male rotifers are smaller,  and their survival lasts just   long enough to allow them to fertilize eggs.

So returning our attention to the female rotifer’s   body, we can see the oocyte in the ovary, nested  in a tissue called the vitellarium. When food   is plenty, the vitellarium can provide RNA,  protein, and liquid droplets to the oocyte, so   that it swells and swells, pushing the rest of the  organs around until finally the egg is released.  The last stop on this tour de rotifer is the  foot, which even extends into a toe. But unlike   our toes, the rotifer toe has a cement gland  in it, producing a glue that keeps the rotifer   stuck to whatever surface appeals to them.

At least, that’s the case for many rotifers,   as they stretch out from a single anchor  point and put their frantic crowns to work.  But some rotifers don’t want to be tied down. They  prefer a more mobile lifestyle. These planktonic   rotifers might end up in the open waters where  there isn’t much vegetation to crawl around on   or to stick to.

So they just don’t.  They might forego a foot altogether.   Instead, they swim around, on occasion even  using the cilia on the crowns to help them.  But if they bump up against a predator or  something else that makes them uncomfortable,   they can do something you might not  usually imagine rotifers doing. They jump.  They can do this because they have paddles. To  see them, we have to return to where we started,   to the front of the rotifer, where these striated  blades make up the planktonic rotifer’s jumping   apparatus.

They work incredibly quickly,  taking only about 7 milliseconds to get going   if a rotifer has made contact with a predator. As we’ve travelled through the rotifer’s body,   we’ve seen just how much can be made with so  little. And should we live in a future filled with   resurrected ancient rotifers and robotic modern  ones, then perhaps we will appreciate them—not   for the cute tardigrades they aren’t, but for the  intricate little living machines that they are.  Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.  And thank you to Surfshark  for sponsoring this episode.  Streaming rights are complicated and some of  your favorite shows might not be available to   you based on your location.

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