Wednesday, September 1, 2010

YPM ICH 13045: Art imitating eel scales

I am no artist, but I do remember a technique I learned in a middle school drawing class called cross hatching. This eel, YPM ICH 13045, is a cutthroat eel of species Synaphobranchus kaupii, and was collected on July 29 2002 by Jon Moore at a depth of 1388 meters at Bear Seamount, an underwater volcanic mountain in the Atlantic Ocean off the coast of New England. Its scales remind me of cross hatching:


Cross hatching is used in drawings to create dimension, depth, and texture. Here are two examples of it that I found using Google image search at this site and this site, respectively:



In a previous post I talked about convergent evolution, which is the phenomenon where similar biological traits and forms evolve in unrelated lineages. A great example of convergent evolution is the wings of birds and bats-- although they both have wings, their wings evolved independently. It is not a trait that they both have through common ancestry.

Cutthroat eels tend to dwell on the slopes of continental shelves, where it might be useful to have scales that create texture to blend in with habitat there (I couldn't find any studies discussing the function of the scales, but this is my hypothesis. If you're wondering if light penetrates at these depths, see the discussion in the comments below). As I mentioned above, artists use cross hatching to create texture in their drawings. These eels have perhaps evolved criss-crossed scales to create texture; humans have developed cross-hatching to create texture. I am going to dub this convergent texture creation! (Presumptuously assuming, of course, that my hypothesis is correct...).

Here are more pictures of the scales, along with a full body shot for scale (although these eels can get much bigger than this).




My husband actually thinks the scales look more like the texture of a common type of steel flooring (pictured below), rather than cross hatching. What do you think?

3 comments:

  1. Sunlight does not penetrate to the depths in which this organism lives, so I find it hard to digest that the scales are shaped like that for 'blending in'. Could they have some mechanical or sensory-enhancing function?

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  2. If you go take a look here - http://archive.serpentproject.com/view/classification/family_59.html - You can see some video footage of S. kaupi swimming on the sea bed. Incidentally, this is a great site - posts video and images of deep water species captured by cameras and ROVs from the oil industry.

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  3. DPC- Good point. I was thinking about that, too, so I made sure to do some investigating before I posted. Here's what I found: According to the second edition of The Diversity of Fishes by Helfman, Collette, Facey, and Bowen, "Deepsea fishes are 15-30 times more sensitive to light and can detect light down to between 700 and 1300 m, depending on surface clarity" (pg. 397). This is called the "mesopelagic zone", and from everything I can tell, this species lives in this zone, where some light penetrates, at least part-time. Fishbase says that it's usually found at depths of 400 to 2200 m. In addition, we have specimens here at the Peabody that were collected at depths as shallow as 329 m and 460 m (as well as specimens collected at deeper depths).

    So while I'm certainly no expert on deepsea fishes, I think given the fact that some light does penetrate at depths where Synaphobranchus kaupii is found, it's at least a plausible hypothesis. That said, I don't know if it's correct! The scales could have no function, or like you said, maybe a mechanical or sensory function. I would be excited to see a study done on the topic...

    Oh one more interesting thing as I re-read this section of The Diversity of Fishes. It notes that mesopelagic fishes have very large eyes to increase their ability to capture light-- something that this species definitely has!

    Chris- Thanks for the link to the videos!

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