This paper reviews the anatomical, physiological, and behavioral studies carried out on polarized-light vision in spiders. This invertebrate group has a variable number of simple eyes, according to the family. The eyes are designated as principal eyes or anterior median eyes (AMEs), and the other pairs, called secondary eyes, are the anterior lateral eyes (ALEs), the posterior median eyes (PMEs) and posterior lateral eyes (PLEs). The retinas of these eyes have rhabdomeric photoreceptors. This paper summarizes the arrangement of the two-channel system that could allow some spiders to detect the polarized skylight patterns either in their AMEs or their PMEs. The physiological studies carried out on some species, which reveal the presence of UV and green receptors in the AME retinas are also described. Finally, the behavioral studies that show that in all species of spiders, except in the family Gnaphosidae, the AMEs are functionally related to polarized-light vision, are reviewed. In the case of Gnaphosidae, the polarized-light perception is through the PMEs. Spiders, in comparison with the other prominent group of terrestrial arthropods, the insects, need more research into their anatomy, physiology and behavior related to polarized light.
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