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Low--resolution vision in a velvet worm (Onychophora)
John D Kirwan1, Josefine Graf1, Jochen Smolka1
1Lund Vision Group, Department of Biology, Lund University, 223 62 Lund, Sweden.
The Journal of Experimental Biology
|April 8, 2018
Summary
Velvet worms (Onychophorans) have limited vision, resolving objects only at close range. Their unique eye structure provides coarse spatial resolution, sufficient for finding shelter but not for identifying prey.
Area of Science:
- Evolutionary biology
- Vision science
- Zoology
Background:
- Onychophorans (velvet worms) are evolutionarily significant due to their simple eyes and relation to arthropods.
- Their visual capabilities remain largely unexplored despite their importance in understanding vision evolution.
Purpose of the Study:
- To assess the spatial resolution of the onychophoran *Euperipatoides rowelli*.
- To understand the relationship between eye anatomy and visual performance in velvet worms.
Main Methods:
- Behavioral experiments measuring responses to dark objects.
- 3D reconstruction and anatomical/optical examination of the eye.
- Computational modeling of visual capabilities.
Main Results:
- *E. rowelli* can resolve stimuli with similar luminance to the background.
- Estimated spatial resolution is 15-40 degrees, depending on contrast sensitivity.
- Eye anatomy, including lens shape and photoreceptor arrangement, limits high-acuity vision.
Conclusions:
- This study provides the first evidence of resolving vision in onychophorans.
- The coarse spatial resolution is likely sufficient for navigation and habitat selection.
- Velvet worms likely do not use vision for prey or conspecific detection at distances beyond a few centimeters.
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