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https://www.intechopen.com/chapters/62301
This episode is sponsored by Wren, a website  where you calculate your carbon footprint.   And you can also sign up to make a monthly  contribution to offset your carbon footprint   or support rainforest protection projects.

When you are in the world of microbes, it does not  seem necessary to think of the largest land mammal   on earth. What could elephants possibly have to  do with a ciliate?

When you say this out loud,   any potential connection seems dubious at best. However, if you look at the Dileptus,   you see an elongated, moving body, one that  seems like it’s made up entirely of snout—like   an elephant’s trunk, disembodied and shrunk  down so that it can survive all on its own.  But unlike the elephant, Dileptus is no gentle  giant. It isn’t moving around because it wants   to play or drink water.

No,the dileptus is  waving around because it is loaded with toxins   and it wants to put them to good use. Now, this may be surprising given its   general blob-like appearance, but the dileptus’  body is divided into two distinct regions:   the proboscis and the trunk, which is confusing  because the trunk on the dileptus is not actually   the elephant trunk-like part of the organism. The trunk is, in this case, more like the trunk   of a tree, it’s the base for the rest of the  dileptus’ body.

The proboscis is the snout, the   part that extends to the rest of the microcosmos  and examines it, looking for something to eat.  And interestingly where the proboscis and  the trunk connect lies the dileptus’ mouth,   a cavity lined with hair-like cilia that continues  down the length of the proboscis. The dileptus can   use these cilia to generate currents in the  water that carry food to its oral cavity. You   can imagine it a bit like if your arm hairs could  stir up the air around you and levitate the snack   in your hand all the way to your mouth.

Which,  now that I’m thinking about it, sounds amazing.  But before the cilia can work their  magic, the dileptus has to catch its food.  And that’s unfortunate for the Spirostomum at  the bottom left corner. It does not know that   on the other side of that piece of debris is  a predator that one scientists called “the   king of beasts among the ciliated protozoa”  with an appetite that is quote “insatiable.”  The dileptus is not a subtle, lying in wait kind  of predator. It’s always moving, always seeking.   And when its proboscis makes  contact with the spirostomum,   it grabs a chunk of its body almost instantly.

The spirostomum is large and nimble,   and it pulls away quickly as if it’s been stung.  But it leaves behind a tasty morsel of itself,   which the DIleptus draws in until it’s  close enough to open wide and eat.  And from its safe distance away, the spirostomum  may not be whole again yet, but it is at least   out of reach of the dileptus, and of its  proboscis, and its hundreds of toxicysts.  You can actually see those toxicysts  here, when we look at the proboscis with   1000x magnification. And while the proboscis’  movement through the water may seem like a chaotic   mess of twisting left and right and up and down,  there is a surprising order to it all--driven by   the placement of those toxic cellular weapons. The dileptus has to move in a way that lets it   immediately attack its prey upon contact, but  its proboscis is only lined with toxicysts   on one side--the side that leads to the oral  cavity.

So it always sweeps its proboscis   with its toxicysts facing whatever is about to be  swept. And when it’s done moving in one direction,   the dileptus rotates its proboscis  and sweeps in the other direction.  Again, this is all so that when the dileptus  finally hits something, it won’t just make   contact: it will unload needles full of  toxins into whatever it has made contact with.  To learn a bit more about how these toxins work,  in one experiment, scientists filled a fluid with   the material coming from the Dileptus’ toxins.  They then placed some Paramecium into the fluid   to see how they would respond. They did not respond well.  Immediately, the paramecium tried to mount their  own defenses by releasing their own harpooning   trichocysts.

Now, that might have worked  against an actual dileptus, pitting ciliate   against ciliate as they poke each other for  survival. But in this experiment, with the toxins   permeating the fluid, the best the paramecium  could hope for was to delay the inevitable,   to use its trichocysts as a temporary fence  until eventually, it emerged to its own death.  Now, that is an extreme situation, one that  a paramecium would probably not actually find   itself in were it anywhere else but in a lab.   Fortunately for paramecium, we do not live in a  world full of Dileptus toxin fluid. Those toxins   are kept safely packaged within the organism  themselves, waiting for their designated time.  Which does lead us to a final question—one  that we do not have an answer for,   but that we like thinking about nonetheless.

We’ve seen the dileptus as a solitary organism,   and we’ve also seen it in groups with others of  its kind. But how? How does an organism that is so   simple, so reactive, so toxic—how is it able  to just casually entwine itself with others   of its own kind?

How can they gather without  immediately all jabbing each other to death?  Well, we don’t know, but it means that there must  be more to the release of toxicysts than just the   simple mechanical stimulus of touch—that there  must be some sort of recognition that makes it   possible for two Dileptuses to know each  other. You might even call it chemistry.  Now, we don’t know the underlying signs and  signals that make that recognition possible.   But what drove this mutually assured safety  may have actually been something selfish.  Imagine for a moment that the palm of  your hand was covered in toxic needles,   and every time you touched your own body, your  palm tore off a piece of it. You would probably   not last long as an organism.

You would need  some kind of way to tell your palm that the   thing it is touching is in fact the body  it belongs to and to not try and damage it.  The same may have been true for the ancestors  of Dileptus and of other organisms that have   toxicysts. They may have kept accidentally hurting  themselves over and over, often beyond repair   until evolution provided a new path, one where  they would be able to recognize themselves—and   perhaps eventually, even others of their own kind.  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 footprint, and then offset it   by funding projects that plant trees and  provide clean-burning fuel and cookstoves   for refugees in Uganda.

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