More on sea urchin vision

This entry is part 6 of 12 in the series Bestiary


If you were intrigued by the description of sea urchin vision in my poem about the purple sea urchin, check out “Tube vision” at the indispensible Creaturecast blog.

Are sea urchins reacting to the presence or absence of light, or do they actually have spatial perception? Recent work by Blevins and Johnsen (2004) and Yerramilli and Johnsen (2009) suggests the latter. In these experiments, urchins would react to the presence of dark targets that looked like nice holes to crawl into in their tank. But they only recognized them if they were above a certain size, implying that their visual perception has a resolution of that certain size, and that they’re not just recognizing simple light or dark cues.

I still can’t get over the weirdness of seeing with one’s arms and legs.

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Dave Bonta (bio) crowd-sources his problems by following his gut, which he shares with 100 trillion of his closest microbial friends — a close-knit, symbiotic community comprising several thousand species of bacteria, fungi, and protozoa. In a similarly collaborative fashion, all of Dave’s writing is available for reuse and creative remix under a Creative Commons Attribution-ShareAlike 3.0 United States License. For attribution in printed material, his name (Dave Bonta) will suffice, but for web use, please link back to the original. Contact him for permission to waive the “share alike” provision (e.g. for use in a conventionally copyrighted work).


  1. I’ve always loved those freakish images of Kwan Seum Bosal (Quan Yin) with eleven heads and a thousand hands and eyes, each hand containing an eye. What better way to illustrate the concept of “lending a hand” the precise moment you see someone in need?

    Maybe sea urchins have a stronger bodhisattva nature than humans do in this regard.


    1. Lorianne, that’s exactly what I was thinking when I wrote my poem! I ultimately decided against including that image, because I wasn’t sure enough readers would be familiar with Guanyin iconography, but I sure wanted to work that in.


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