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Kidnapped Sea Snails

There are many kinds of amphipods in the world. (Bathyporeia, Flickr)

If your skin gets irritated from using bug repellant, what fixes do you use? There are candles, but you can't really get in a hike walking around holding a lit citronella candle. Some people I know drench their backpacks in bug repellent and hope that does the trick.

Amphipods And Pteropods

If you're someone who's tried that last one, you have something in common with Amphipods. Amphipods, shrimp-like crustaceans living in the Southern Ocean, hold other animals called pteropods--a planktonic mollusk also known as sea snails, sea angels, or sea butterflies--on their backs like backpacks and use them as a living shield.

The sea snails secrete a poisonous chemical that deters predators like cod icefishes. Amphipods are unaffected by the chemical, and when they carry the sea snails on their backs, they're also protected from predators. Icefishes quickly realize the amphipods carrying pteropods piggyback don't make a great snack, so they learn to avoid them.

Once the pteropods are in the clutches of the amphipods, they can't hunt to feed, so they starve to death. As far as researchers can tell so far, the sea snails don't benefit at all from the association.

Thank you to Deneb Karentz of the University of San Francisco for reviewing this episode's script.

Sources And Further Reading:

  • Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research. "'Kidnapping' in the Antarctic animal world? A puzzling relationship between amphipods and pteropods." ScienceDaily. September 10, 2018. Accessed November 13, 2018.
  • Katz, Brigit. "Kidnapper Crustaceans Use Tiny Mollusks as Unwitting Shields." September 14, 2018. Accessed November 13, 2018.
  • McClintock, James B. Janssen, John. "Pteropod abduction as a chemical defence in a pelagic antarctic amphipod." Nature: International Journal of Science. Nature volume 346, pages 462–464 (02 August 1990). Accessed November 13, 2018.

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