Omega iris
From Wikipedia, the free encyclopedia
Omega iris (also known as omega eye) is an unusual iris structure found in many armoured suckermouth catfish. The top part of the iris descends to form a loop which can expand and contract; when light levels are high the loop expands to cover the center of the pupil giving rise to a 'c' shaped light transmitting portion.
This feature gets its name from its similarity to the symbol for the Greek letter omega (Ω), as the loop of the iris resembles the loop above horizontal bars in the capitalised letter. In the usual orientation of the fish the letter would appear to be upside down.
The origins of this structure are unknown, but it has been suggested that breaking up the outline of the highly visible eye aids camouflage in what are often highly mottled animals[1].
[edit] References
- ^ Douglas, Ron (2002-08-08). The eyes of suckermouth armoured catfish (Loricariidae, subfamily Hypostomus): pupil response, lenticular longitudinal spherical aberration and retinal topography. The Journal of Experimental Biology.
[edit] External links: Pictures of the eye of various suckermouth catfish
- http://maxstrandberg.com/freshwater/catfish/bristlenose_male.htm ancistrus species - loop small
- http://maxstrandberg.com/freshwater/catfish/starlight.htm ancistrus species - loop enlarged (view of fish from front)
- http://www.malawicichlidhomepage.com/other/panaque_nigrolineatus_l190.htm numerous pictures of panaque nigrolineatus showing the feature
- http://maxstrandberg.com/freshwater/catfish/gibbiceps.htm close up photograph of Glyptoperichthys gibbiceps eye (species now renamed)
