Armored Up

“When caught out in the open and vulnerable, this octopus does something truly extraordinary,” David Attenborough narrates. In Blue Planet II, Season 1 Episode 5, the camera captures a strange and fascinating sight: a common octopus (Octopus vulgaris) swiftly surrounds herself with a pile of shells, creating an impenetrable armor to shield herself from the attacking pyjama shark.

In nature, the use of tools is a sign of cognitive sophistication. The ability of the octopus to create a shield for itself is unique, but not outlandish in the context of cephalopods. The cephalopod class contains species (including Octopus vulgaris) with the most developed nervous systems among invertebrates, comparable to even advanced vertebrates [1]. A significant number of these species have demonstrated some form of tool use. This is especially noteworthy because aquatic habitats, by nature, are not conducive to tool use due to a scarcity of tools [2]. Unlike land animals, aquatic tool users tend to fashion their tools out of other animals and their products [2]. Octopus vulgaris is not the only species that fashions shields. The Veined Octopus, Amphioctopus marginatus, lives in the soft sediment off the coast of Indonesia. These octopuses carry around coconut shell halves that they arrange into a defensive shelter when necessary [3]. The octopus does not gain any benefit from the shells while it is carrying them around. The only benefit is the future potential shield that they could make when faced with a predator [3]. This demonstrates incredible foresight and planning by the octopus.

So how did octopuses come to be so smart? Researchers have uncovered a process called RNA editing, whereby mRNA is altered by enzymes post-transcription. While RNA editing is found in metazoans, it is unusually extensive in cephalopods, especially squids and octopuses [4]. Researchers believe this uniquely substantial RNA recoding can help explain why cephalopods have evolved such highly developed brains, leading to enhanced intelligence and the ability to create advanced tools. So, a piece of advice to all the pyjama sharks out there: don’t underestimate your shield-wielding foe!

by Kathy Li, Megan Jiang and Eric Yu

Blue Planet II, S1E5: Green Seas, starting at 5 minutes and 25 seconds from beginning. 


  1. Shigeno, S., Andrews, P.L.R., Ponte, G., Fiorito, G. 2018. Cephalopod brains: An overview of current knowledge to facilitate comparison with vertebrates. Physiol. 9: 952
  2. Mann, J., Patterson E.M. 2013. Tool use by aquatic animals. Trans. R. Soc. Lond. B. Biol. Sci. 368(1630): 20120424
  3. Finn, J.K., Tregenza, T., Norman, M.D. 2009. Defensive tool use in a coconut-carrying octopus. Current Biology 19(23): R1069-R1070
  4. Liscovitch-Brauer, N., Alon, S., Porath, H.T., Elstein, B., Unger, R., Ziv, T., Admon, A., Levanon, E.Y., Rosenthal, J.J.C., Eisenberg, E. 2017. Trade-off between transcriptosome plasticity and genome evolution in cephalopods. Cell 169(2): 191-202.

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