Polarization Vision in Cephalopods: Neuroanatomical and Behavioral Features that Illustrate Aspects of Form and Function

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Abstract
Polarization sensitivity (PS), which arises from the orthogonal arrangement of microvilli in the retina, has long been known in shallow-water cephalopods. Micrographs presented herein signify that some deep-water cephalopods may also possess PS. Precise measurements of the angles of microvilli in the retinas of shallow-water octopus, squid and cuttlefish revealed neuroanatomical differences that may explain variation in the limits of polarization angular discrimination in different species and habitats. A question yet unanswered is whether cephalopods can discriminate between polarization and intensity. Recent behavioral experimentation has illustrated that one clear function of PS is enhanced predation: it enables better detection of transparent, opaque, or silvery-reflecting prey. The use of PS for navigation in cephalopods is still controversial, and our recent experiment on squids failed to support this notion. It is possible that cephalopods show polarization patterning produced in their skin as a mode of communication that cannot be detected by polarization-insensitive predators such as many fishes and marine mammals.