Tiny snail swims like a bee flies

Limacina helicina, a mini sea snail, moves using "underwater flight," write researchers in the Journal of Experimental Biology.

Sea butterfly at different stages of wing beat. Photo: David Murphy.

Sea butterfly at different stages of wing beat. Photo: David Murphy.

In a remarkable example of convergent evolution, we show that the zooplanktonic sea butterfly Limacina helicina ‘flies’ underwater in the same way that very small insects fly in the air. Both sea butterflies and flying insects stroke their wings in a characteristic figure-of-eight pattern to produce lift, and both generate extra lift by peeling their wings apart at the beginning of the power stroke (the well-known Weis-Fogh ‘clap-and-fling’ mechanism). It is highly surprising to find a zooplankter ‘mimicking’ insect flight as almost all zooplankton swim in this intermediate Reynolds number range (Re=10–100) by using their appendages as paddles rather than wings. The sea butterfly is also unique in that it accomplishes its insect-like figure-of-eight wing stroke by extreme rotation of its body (what we call ‘hyper-pitching’), a paradigm that has implications for micro aerial vehicle (MAV) design. No other animal, to our knowledge, pitches to this extent under normal locomotion.

The BBC reports that new camera technology made the discovery possible.

To make the discovery, Dr Murphy and his colleagues used a system they call tomographic particle image velocimetry: four high-speed cameras trained on a tiny volume of fluid, which is illuminated with laser beams and seeded with shiny particles to trace flow movements.

"Using our four cameras, we make a 3D measurement of the flow that the animal produces as it's swimming," he explained.


Notable Replies

  1. Some organisms have no shame.

    [note sarcasm]

  2. This discovery is just satisfying on so many levels.

    Zooplankton gotta flap, bee gotta fly
    Evolution converges and you know why?
    Natural Selection is coming to town...

  3. ...but fruit flies like a banana.

  4. Odd, isn't it? This little animal is far more interesting and attractive than Trump, but which thread gets all the comments? Perhaps it should issue a PR statement about its plans to get all the blue-green algae out of the Pacific and make them build a wall.

  5. It is a lovely example of convergent evolution; but also interesting because it is apparently very much the exception: moving in a (relatively) viscous fluid where achieving neutral buoyancy is fairly easy is rather unlike flying in air; and apparently most of this curious beast's colleagues take advantage of that and don't do it this way.

    It'd be fascinating to know why this particular one uses a wing strategy rather than paddling; as well as how the efficiency compares.

    It sure is eerily bee-like in silhouette, despite the whole 'has a shell' thing.

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