Rhynchohyalus Natalensis: Four-Eyed Deep-Sea Barreleye Fish Has 360 Degree Vision
    By Hank Campbell | March 28th 2014 06:00 AM | 4 comments | Print | E-mail | Track Comments
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    The Rhynchohyalus natalensis in a recent paper was caught about 1000 meters under the Tasman Sea and it has two pairs of eyes, allowing it to spot danger from every angle. One pair is upward-facing tubular eyes, to spot danger from above, while another set is on the side of its head, to detect bioluminescence from deep sea creatures.

    The second type of eye is typically associated with invertebrates. The authors write that this is only the second instance in a vertebrate, after Dolichopteryx longipes, with both reflective and refractive optics.  

    I particularly liked the description of how they modeled the optics and image focusing. The authors have the same question I have; this is cool, so why isn't it more common?

    Gross morphology of the eyes of R. natalensis. (a) Lateral view of specimen shortly after capture; (b) dorsal view of head showing the spherical lenses of the dorsally directed tubular eyes; (c) ventral view of the head showing the silvery lateral walls and the dark cornea of the diverticulum—the red arrows indicate a medial notch in the diverticular cornea, enlarging the visual field caudo-medially; (d) lateral view of the right eye—note the reflection of the flashlight (blue arrow) from the diverticular mirror located inside the eye and observed at the time of collection; (e) MRI section of the right half of the head showing the tubular eye including the lens and the lensless diverticulum; (f) 25 μm thick resin-embedded histological section of the eye with the lens removed. In (d,e) the margins of the ventro-laterally facing diverticular cornea are indicated by arrows. Credit:  DOI:10.1098/rspb.2013.3223

    Citation: J. C. Partridge, R. H. Douglas, N. J. Marshall, W.-S. Chung, T. M. Jordan, H.-J. Wagner, 'Reflecting optics in the diverticular eye of a deep-sea barreleye fish (Rhynchohyalus natalensis)', Proc. R. Soc. B 7 May 2014 vol. 281 no. 1782 20133223 DOI:10.1098/rspb.2013.3223


    this is cool, so why isn't it more common?
    There is only so much mileage to be got out of “dissing” William Paley.
    Robert H. Olley / Quondam Physics Department / University of Reading / England
    Really? I honor tradition, if dissing Paley was good enough for Darwin and The Lancet, who am I to argue? But my question was serious. It would seem like these eyes have substantial benefit.

    this is cool, so why isn't it more common?

    It would seem like these eyes have substantial benefit.

    I had to look up Dolichopteryx longipes
    - It's the Brownsnout spookfish.  What a wonderful name.  There must be a lot of spooks who wish they could monitor us with eyes like that.  ;-)

    As to benefits - there would be a cost in processing power.  If the images are processed in parallel then nerve cells which might be used for another purpose must be dedicated to the optical processing of almost double the data which otherwise similar fish have to process. 

    Alternatively, if the signals are in some way multiplexed there would be a loss of speed of response to stimuli.  The switching between channels would be measured in milliseconds so there would be milliseconds of signal blanking between signal processing events.  Win some, lose some.

    On balance I would say that those eyes fill a precisely defined niche, but in general a rapid response to stimuli would outweigh an ability to detect more stimuli.

    Just a quick off-the-cuff theory, of course.
    Oh dear — it seems like I pulled the wrong leg there.

    I only recently learned that the eyes of trilobites contained mineral lenses made of calcite.  However, sticking to camera lenses, well known in vertebrates and cephalopods, I read in Life's Solution: Inevitable Humans in a Lonely Universe by Simon Conway Morris that they are also found alcopids (a group of marine annelids) and also cubozoans or Box jellyfish, which do not have a brain but
    are active and highly and highly agile swimmers, have obvious visual acuity, and uniquely for cnidarians engage in bouts of copulation.
    There are other ways of dealing with low light though.  Mormyrid fish which live in murky rivers use electricity, and for this their cerebellum is so developed that their brain-to-body weight is similar to that of humans.  Their environment makes me think of the Paralympic sport Goalball (though actually I first made the connection the other way round.)

    Robert H. Olley / Quondam Physics Department / University of Reading / England