The cockeyed strawberry squid

August 14, 2015 • 1:45 pm

The strawberry squid (Histioteuthis heteropsis), also known as the cock-eyed squid, is famous (as you can also tell if you parse the Latin binomial) for the huge disparity in the size and form of its two eyes. That’s evident from this gif:


Now, before you watch the explanatory video below, or read Wire‘s recent piece on its eyes, form an evolutionary hypothesis about the disparity—one that involves natural selection. How could you test it?

Think! (It’s not obvious, and of course the explanations you’ll hear are speculative). The truth is, what the video and article say sounds good, but we have no idea if the form of natural selection they suggest really acted to produce this bizarre morphology.

Okay, watch the video, and then read the piece above.

And remember, folks, squids, like all cephalopods, are molluscs—in the phylum Mollusca.


27 thoughts on “The cockeyed strawberry squid

  1. The strawberry and the strawberry squid, yet another example of convergent evolution. Now, how do the squid taste, and could they be made into a milkshake?

    1. I’m reminded of a line from a song in South Pacific: “…so they call me a cock-eyed octopus…”

  2. There does seem to be a lateral “top” and “bottom” to this creature, and with such distinct organs of vsion, it does look like something that must survive based on stimulus from two different worlds. Is it relying on two different food sources, or does it keep one eye on danger, and the other on lunch?

  3. Some nocturnal owls have asymmetrical ear openings, one higher than the other, allowing them to localize a sound source based on the difference in arrival time.

    It seems reasonable that this trait was a result of natural selection, with the location of the ear openings changing gradually across generations as benefit accrued.

    By analogy one could explain the difference between the size of the squid eyes using a similar mechanism.

  4. I didn’t foresee the up/down asymmetry but rather guessed that the squid had different needs for optic systems and so had diversified the eyes. The up/down asymmetry I know of are fishes that lie ambush on insects and so have split optics for water/air.

    Testing an evolutionary hypothesis here would involve covering one eye and see how the squid fares, I guess. It would help if the researchers have a hypothesis on why the selection happened,* as in the video.

    * Moran safeguard: it could still be near neutral drift, especially if it was a population bottleneck. (Yeah, right. =D)

  5. I’m happy any time I see a brown human eye as “your” eye. I have brown eyes, as do almost all of the human population, yet time & again science & even evolution science sites, videos, photos, etc. depict a blue eye.

    Blue-eyed people are mutants! And as Ken Ham has pointed out there’s no such thing as a beneficial mutation!

  6. I notice than this squid shows a tendency to stay vertically in the water, head down, but not exactly vertical: it is tilted in such a way that its right eye looks up and its left one looks down. And the animal turns on itself to sweep the water around. This tilt orientation could be at start purely accidental and then generalized for the whole population by genetic drift (I wonder if human righthandedness started like that). As soon as the “tail left, head right” tilt is well established in the population, the selection can act differently on each eye.

  7. Their explanation for the specialized eye seems reasonable. Given that other deep sea creatures also have have pigments in their eyes to absorb blue light (to better detect prey against a blue background), the use of the similar eye in this squid could be similar. But why the conventional eye as well? Perhaps this is a squid that ascends to shallower depths, and the other eye is useful in that environment. Having two eyes that are equipped to be useful in both deep and shallow water would mean compromises — they would not be so good at depth, nor in shallow water. But the different eyes means they can optimize for each condition.

    1. If I understood you correctly, you’re suggesting that it hasn’t evolved a single hypertrophied eye, so much as it’s evolved a single atrophied eye?

  8. The question which occurred to me on seeing this is – does the squid always develop with hypertrophy of the left eye, or is it more-or–less randomly distributed between left and right eyes? Same problem as with flatfishes of various sorts (but not skates and rays).
    From the article, I see that it’s not just hypertrophy of the eye, but a suite of other changes too. But given the transcranial voyages of the flatfishe’s eye, I don’t see that developmental difference as an insuperable issue.

        1. lol – I think “blue blistering barnacles” would involve a lot of spitting as in “suffering succotash”;-)

  9. Loving all these recent posts on eyes 🙂

    Also interesting to note – the optic lobes of the squid are different sizes, with the larger lobe connected to the larger diameter eye.

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