Symsagittifera roscoffensis

I have the chance to live by the sea in the north west of France, in Brittany. Here, it’s quite easy to sample Symsagittifera roscoffensis directly on the beach during the low tide. They basically look like this under the foldscope :

These free-living acoelomorph worms, formerly called Convoluta roscoffensis, have a characteristical green color because they contain microalgae named Tetraselmis convolutae. And because of this symbiosis, they are naturally attracted by light in order to feed the algae inside. It’s a phototaxis organism as you can see on this simple video I made. Time is about 2 minutes :


4 Comments Add yours

  1. laksiyer says:

    Such a fantastic set of videos.. Just love the second one. I am lost in thought about what might be the evolutionary basis for this association.. Did the worm naturally move towards light and thus became a vessel for the alga to grow, or did the alga parasitize the worm and somehow messed with its brain to move towards light?? Thank you so much for this, just made my day.

  2. Manu Prakash says:

    What a fantastic way way to introduce yourself to the foldscope community @Thibaut!! Wow wow wow. Just floored. Where in the body do the algae anchor? Do they divide inside the worm? We need to learn association of algae with metazoans; to have the coral survive. Maybe, this could be a good “model system” since coral are so hard to do quantitative (molecular) biology on.

    Can we find them in California. Can you please make a few more foldscope videos.. looks like you have millions of worms!!

    Thank you ; thank you.. you have just won Internet 😉


  3. tpollina says:

    I have updated the post by adding two more videos using the foldscope which are quite better than the first one!

    @Laksiyer, The statocyst and the pair of ocelli of this worm, connected to a simple nervous tissue, grant him the faculty to orient itself in the three dimensions, and to react to a variation of luminosity. And because of this faculty to feel the light, the worm will naturally orient itself to the light to feed the algae inside and to let them grow. I’m so happy to have made your day 😉

    @Manu !! I was walking on the beach and they were just under my feet ! I was so impatient to have a look under the foldscope !! I’m now cultivating them, even if someone in Roscoff is already doing a lot of stuff on it (And I guess things regarding the coral bleaching); his name is Xavier Bailly.
    I have found a paper that explains things because I wasn’t sure about the cycle of life. Here is a diagram :

    Juveniles, initially whitish, herbivorous, ingest unicellular green algae. Some of these algae are not digested, but conducted under the ectoderm. In adults, the pharynx and the entire digestive system regress. The algae divide and proliferate inside the worm, which turns green! His diet and breathing are entirely dependent on photosynthesis: he assimilates only the sugars of the photosynthetic cycle.

    They look endemic to the French coasts but I could bring some if you want to have some cultures in the lab !?

    Some other interesting papers :

    I’m so happy and proud to be in the FoldScope Community!
    Thank you for this fabulous welcome !


  4. Manu Prakash says:


    1) Let;’s talk on the phone tomorrow.

    2) Wonderful videos. I noticed a zone in the organism (near the head) where very few algae make it. Does that mean some signals exist that indicate that this tissue niche is not accessible to the animal. That would be interesting to think about. What signals tell the algae this is a no-go zone.

    3) I found one paper on some collective behavior on this worm. I saw the spinning and collective migration in your video; and that might be coming from somehow the worms communicating to each other. See the link; it’s a very basic paper but a good start:

    4) I find it wonderful that every worm has to start by ingesting some of the algae to start the cycle. How fascinating. Yes; do bring a few when you are coming. Let’s have you come asap..


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