Spatial Vision in a Flat World: Optical and Neural Adaptations in Arthropods

We review evidence to show that in several arthropod families eyes and supporting neural control systems are shaped according to the spatial layout of their environment Amphibious crabs that live at sandy beaches and mudflats and insects that live above or below the water surface have horizontally aligned acute zones for vertical resolution in those eye regions that look at the horizon. In amphibious crabs acute zones are aligned with the horizon by visual, leg — proprioceptive and statocyst reflexes whereby optokinetic sensitivity to movement around roll and pitch axes reaches a sharp maximum at the eye equator. There is clear evidence of a position dependent mechanism of eye alignment to the horizon in at least two species of flat world crabs. Optokinetic sensitivity to movement around the yaw axis is restricted to the dorsal visual field in flat world crabs and in waterstriders with a maximum just above the eye equator. We discuss the relevance of these specialisations for spatial vision in a flat world