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 nonmotile 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,
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