Of The Walking Dead, Cosmos, and Planaria

Last Sunday there was an unexpected nerdy treat for us planarian enthusiasts in the US. Our favorite wormies were mentioned in not one, but two TV series, coincidentally, both at 10 pm. I watched one of the shows as it was broadcasted and I saw the second one yesterday night as a rerun.

The two shows that mentioned planarians were The Walking Dead, a dystopian story set in a world in the midst of a zombie apocalypse and Cosmos, the remake of the famous ‘80s documentary series by Carl Sagan, this time hosted by Neil DeGrasse Tyson.

I watched The Walking Dead (TWD) first (and I bow my head in shame… not really). I am a TWD fan, which is remarkable because I do not like the terror/gory/zombie/slasher genre, not even a little bit. My wife “infected” me with TWD, but I digress. Their mention of planarians was in a scene where a girl talks about using planarians in science class. That’s it, but it was really cool to hear it (NERD – And proud!).

As for Cosmos, well, I have a little bone to pick with it.

Do not get me wrong, I am loving the series and I intend to keep watching it. Good job!

Now about planarians… first, this is what they usually look like:

planaria blogpost

In Cosmos there was a simply magnificent segment on the evolution of eyes. Really cool! The thing is that when they showed a flatworm, it looked like a planarian, yet it was show swimming with undulating movements (and rather fast too). Planarians do not move like that; they do not really swim either. Here is a clip from another show, “The Shape of Life” that shows actual footage of how a typical planarian moves (at approximately 4:46 to 5:15. Note: they explicitly talk about planarian reproduction, etc.).

By the way, they actually sped the video mentioned above; planarians are really slow. Here is a video played at normal speed that shows how they really move.

However, the Cosmos segment got the movement right, just not the planarian movement. The type of worms that swim like that are another type of flatworms, called polyclads. These guys include some of the most beautiful animals out there.

Picture credit: eol.org and the authors of the picture.

Swimming polyclads are shown in The Shape of Life video as well. That’s the type of movement that Cosmos showed. Polyclads also have the distinction of being the type of flatworms with the most complex brain. In fact, they were the subject of really interesting experiments of nerve and brain transplantation, which for some reason as far as I know, have not been followed up.

Cosmos and TWD are only the latest two of various TV shows and other examples of popular culture that mention planarians. Want to know more? Well, I talk about some of them in my book! By the way, I “tweeted” NDT pointing out the mistake and never got an answer… Sagan would have replied.



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  1. Personally, I thought the use of polar bear divergence from brown bears and the evolution of eyes to explain evolution by natural selection was brilliant. Bringing up artificial selection of dogs in this context was also brilliant. Everyone is vulnerable to making mistakes. If you noticed an honest mistake, you would be doing a disservice not to tell them because the point of science is to promote the truth, it is more important than being right.


  2. I think the writers and researchers of Cosmos–reborn would ‘love’ to hear from you. Incorrect presentations will on occasion come to haunt the presenters. The original presentation from 30 years was and still is timeless. I am, currently, holding my critique and hoping that the most impressionable find their way with Dr. Tyson.


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