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Lee Goldman/Coral Triangle Adventures LLC

The coral reefs of the Philippines house many eye-catching marine wonders. However, few are as absurd-looking as the boxer crab or pom-pom crab (Lybia tessellata). This tiny crustacean showcases a unique relationship with sea anemones—one that, at first glance, may not appear to benefit both parties involved.

Growing up to 2.5 cm (1 in) wide, boxer crabs live in the warm Indo-Pacific waters, emerging only to feed under the cover of darkness. They possess chelae (pincers) that are simply too small for defending themselves or even gathering food. Instead, L. tessellata (like other crabs of the genus Lybia) carries a sea anemone in each claw, akin to how a person would carry pom-poms or wear boxing gloves. When threatened, the boxer crab may jab at potential predators, hurting or scaring them off with the sea anemone’s cnidocytes (stinging cells). It’s said that the scent of the sea anemones may also ward off predators, providing the crab with a sort of chemical camouflage. The boxer crab also uses its sea anemones like mops, gathering detritus and food particles from the ground (which it later picks out and consumes).

The specifics of how this relationship benefits the sea anemone are not that clear, though. Some experts say that it guarantees food for the sea anemone, while others theorize that it facilitates their asexual reproduction. A 2017 study supports the latter notion: Researchers observed that when one sea anemone is taken from a crab, it splits the other into two. In a matter of days, the fragments regenerate into new, viable sea anemones—one of the few documented instances of a species inducing asexual reproduction in another. It’s somewhat comforting to know that at least, these sea anemones are getting something out of this recurring indignity. 

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References

  • http://www.tfhmagazine.com/details/articles/a-champion-fighter-the-mosaic-boxer-crab-lybia-tesselata-full-article.htm
  • https://www.jungledragon.com/specie/10653/pom-pom-crab.html
  • https://www.popsci.com/boxer-crabs-thieving-cloning-anemones/
  • https://www.projectnoah.org/spottings/228496016
  • Schnytzer Y, Giman Y, Karplus I, Achituv Y. 2017. Boxer crabs induce asexual reproduction of their associated sea anemones by splitting and intraspecific theft. PeerJ 5:e2954 https://doi.org/10.7717/peerj.2954

Author: Mikael Angelo Francisco

Bitten by the science writing bug, Mikael has years of writing and editorial experience under his belt. As the editor-in-chief of FlipScience, Mikael has sworn to help make science more fun and interesting for geeky readers and casual audiences alike.