Polarization Vision of Crustaceans

This chapter reviews polarization vision in diverse crustaceans with a specific focus on work completed since the 2014 edition of this book. Almost all crustaceans are sensitive to the planar polarization of light. They commonly possess two channels of orthogonally arranged photoreceptors with intrinsically polarization-sensitive ordered microvilli. These two channels are compared to impart linear polarization sensitivity, though ambiguous null points within the system make it impossible to distinguish between different combinations of angles and degrees of polarization. In stomatopods, biological quarter-wave retarders are utilized to bestow circular polarization sensitivity to linear polarization-sensitive photorecep
tors, allowing for circular polarization vision—a sensory modality unique to sto
matopods so far. Crustaceans occupy a wide variety of environments, each with environmental polarization information that may be used by their inhabitants for a variety of tasks including object detection, navigation and signalling. The celestial polarization pattern viewed underwater through Snell’s window offers one such cue, which some crustaceans, including one stomatopod species, have been shown to use for orientation and navigation. Stomatopods also possess body surfaces that reflect linearly and circularly polarized light that they use for intraspecific communication. Despite the progress in polarization vision research across a variety of crustacean species, many aspects, including post-retinal processing of polarized light, how polarization vision interacts with other visual modalities, and what the evolutionary drivers for this sensory modality are, remain poorly understood. By incorporating new technologies and increasing the breadth of taxa studied, we may gain greater insights into these knowledge gaps and a better understanding of the functional uses of polarization vision beyond navigation and communication.