You know, it didn’t have to be this way.  The microcosmos is vast, and there are so  many organisms meeting and interacting with   each other every day.

And things often go  very well for the microbes we watch...they   often live peaceful lives that do not end with  them being gruesomely turned into the external   stomach of a single celled parasite. Heck, we could even be talking about   the ciliate up the screen right now, called the  Nassula.

Only, we could have gone back to when   it looked more like this, the inside of its  body dripping with blue, yellow, and black.  And we could have been sitting here talking about  how Nassula swim through clouds of plankton,   seeking out their next meal of cyanobacteria.  And how, after the Nassula capture and digest   their prey, their cytoplasm fills with the colors  that once belonged to the cyanobacteria. Beads   of blue and blobs of yellow, and sometimes even  bits of pink—a colorful casualty of consumption.  But no. We are not here today to talk  about cyanobacteria and pigments.   We have other matters to discuss.

Because  somewhere else in the microcosmos is this.  I know, it might not look like much, just a pill  with a vacuole opening and closing inside it   while little tufts of hair move on the surface.  This is a suctorian, a type of ciliate,   which makes it a relative of the Nassula. But this is a young suctorian, a larvae.   Eventually, the suctorian will shed its rings of  cilia, and in the process, it will lose both its   family resemblance and its ability to swim around. But that’s not a concern though for the suctorian.   The ciliate that should be more worried is the  Nassula because a hairless suctorian doesn’t stay   bald.

It replaces its cilia with tentacles. And this is what happens next.  Remember, the suctorian can’t swim anymore. It  can’t go seek a ciliate.

But it can sit around   with its tentacles extended, waiting  for the right cilia to come to it.   And when one does, the tentacles go to work,  sticking to and sinking into its target.  In the area around where the suctorian’s tentacles  have attached, the Nassula’s cilia will stop   beating. But it’s just a small portion of the  cilia for now, not enough to stop it entirely. And   so for a time, the Nassula will continue swimming,  seemingly unaware of the suctorian on its back.  For the suctorian, this is a good deal.

It doesn’t  need to swim anymore, it has Nassula to do that.   But the Nassula is more than just  a free ride around the microcosmos.   It is also the suctorian’s next meal.  Sometimes, we are what we eat. And  sometimes, we are what’s eating us.   And with the suctorian attached, the Nassula  becomes more and more difficult to recognize,   looking more and more like a whale with  outsized barnacles protruding from its side.  Near the site where they’ve attached to the  Nassula, the suctorian will begin to digest   bits of their host. This means that the Nassula  now has three uses for the suctorian: a free ride,   a meal, and now, a temporary external stomach.  Like the cilia that stopped beating, this  digestion is localized, allowing the Nassula’s   organelles to contract and the organism to live  as it is slowly being digested from within.  The suctorian doesn’t have an oral cavity  to act as a mouth, but it doesn’t need one.   It has tentacles, which shorten in length and  thicken in width as the suctorian begins to pass   grains of the digested ciliate through  it.

And the Nassula, once kaleidoscopic   with the remains of its own meals, now passes  those colors on to its unwelcome passenger.  For some suctorians, one host is not enough to  satiate its appetite. If you look at the top   corner of the Nassula here, you can see that one  of the suctoria has its tentacle poking outwards,   keeping them extended and ready in case  another Nassula comes along to add to its meal.  And this is not a matter of moving from  one host to the next. No, the suctorian is   happy to attach itself to multiple Nassula,  assembling a crowd of hosts and parasites.  But the suctorian has one more use left for  its host: a nest.

Not a real nest, of course.   Suctorians don’t lay eggs. Instead, they bud,  growing their young out of themselves. And they do   this while attached to their host, sprouting their  young on the outside of their own non-motile bodies   until the new larvae is ready for life on its own.

The baby suctorian is equipped with its own cilia,   able to swim away for its own independent  life. But at the end of the day, suctorians   are parasites. They’re not meant to be on  their own.

So one day, when they’re ready,   those larvae will follow the path of their parent,  settling down for a life on their own meal.  It didn’t have to be this way, of course.  The Nassula could have lived its whole life   without ever having come across a suctorian  parasite. It could have spent its life contentedly   grazing upon cyanobacteria and converting itself  into a multicolored monument to its own meals.   And many Nassula have lived such lives,  meeting their ends in other ways,   perhaps more dramatic or perhaps less. But our world is maintained by these meetings,   by these pigments, these chemicals, this  energy, passing from one organism to the next,   and by the fateful contact of some  patient, outstretched tentacles.  Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.  And thank you of course for all of the support  you’ve shown for this channel over the past two   years that it has existed.

Whether that’s been  through sharing videos with friends and family   or supporting the channel directly by being  a patron on Patreon, or by picking up some   microcosmos merch, like our new tardigrade shirt. Again, that pre-order runs only through August   31st. So, if you want to make sure you get  the color you want before one of them goes   away forever, you’ll have to order before  the end of the month over at dftba.com  This episode, it marks the end of Season 4  of Journey to the Microcosmos, but we will   be back with Season 5, and speaking of  the aforementioned Patreon patrons, you   are now seeing their names on the screen.

If you  like what we do here, and you want to thank us for   this show existing, these are the people you  should be thanking. We appreciate all of them   so much and if you would like to join them, you  can head on over to patreon.com/journeytomicro.  If you want to see more from our  Master of Microscopes, James Weiss,   check out Jam & Germs on Instagram,  and if you want to see more from us,   there’s probably a subscribe  button somewhere nearby.