View Full Version : Acute Zone
Gonodactylus
03/20/2014, 08:59 AM
Yes, juvenile Odontodactylus scyllarus are cute, but that is not the reason I have posted this photo. This shot nicely demonstrates the acute zone of the mantis shrimp's eye where the photo receptors (ommatidia) are all oriented in the same direction providing maximum information about the distance, color, polarization and movement of the target. Over most of the eye, only a few ommatidia are pointing at the same location. We see this in the form of the pseudopupils, the black spots produced when the receptor is pointing at the camera or your eye and no light is reflected back. If the eye is looking above or below the the plane formed by the mid-band, we see just two small pseudopupils. If the ommatidia in the mid-band are pointing at your eye, we see three sets of pseudopupils. Around most of the mid-band, only a handful of receptors are aimed at the target and the pseudopupils appear as slits. However, in a small region in the front of the eye more of the ommatidia are aliened together with the resulting pseudopupils appearing as large dark blotches. When an animal is particularly interested in an object, both eyes are brought to bare on the target and we see six large sets of pseudopupils. Because the eyes are usually in motion independently scanning the visual field, we usually don't see the acute zones of both eyes simultaneously. However, in this case, I placed another stomatopod just below the camera lens. The cavity resident became very interested in the intruder, focused both eyes on the opponent for about a second and then attacked.
Islandoftiki
03/20/2014, 09:13 AM
So, if you lived in the ocean, you would never want to see this phenomenon up close and personal. ;)
Gonodactylus
03/20/2014, 09:30 AM
One species of Odontodactylus (O. brevirostris) takes advantage of this. It's eyes are colored to look like the acute zones are focused on you - even if they are not.
Roy
Calappidae
03/20/2014, 09:52 AM
Sweet! I'm guessing it's very difficult to capture that as they never fully focus longer than a few seconds right?
Gonodactylus
03/20/2014, 12:10 PM
I've taken literally thousands of photographs of stomatopod eyes and maybe one in a hundred displays both acute zones.
Roy
Kharn
03/20/2014, 04:08 PM
Yes I agree!
The Stomatopods tend to do the old "T-Rex" gave, where they tilt their head and have 1 eye staring directly at you giving that effect from 1 eye.
Most noticeable in O.scyllarus likely due to their sheer size in comparison to far smaller species...
O.scyllarus
http://imagizer.imageshack.us/v2/800x600q90/7/syj0.jpg (https://imageshack.com/i/07syj0j)
G.chiragra
http://imagizer.imageshack.us/v2/800x600q90/600/ckhp.jpg (https://imageshack.com/i/gockhpj)
EDIT: I have over 1000 images on my PC stored in only Smasher / Spearer folders xD... takes a bit to find what I want these days :X...
Islandoftiki
03/20/2014, 04:47 PM
I rarely see my O. Scyllarus even look directly at me any more. She almost always comes out of her burrow and up to the glass when I'm there, but the pseudopupils facing me are usually the very outer ones in the upper or lower hemispheres. Now, her damsel tankmate probably gets to see double acute zones all the time with his shenanigans.
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