The Spectral Sensitivity of Photoreceptors and the Screening Function of the Cornea of Greenlings (Hexagrammidae)

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Corneas in different species of the greenling family Hexagrammidae can change coloration depending on the level of ambient illumination. This process is based on redistribution of carotenoid pigments in specialized chromatophores. The spectral properties of corneas and the absorbance spectra of the visual pigments in the retinal photoreceptors were measured in four species and in one inter-species hybrid of greenlings. The modifying effect of the colored corneal filters on the cone absorbance was evaluated. A positive correlation was found between the degree of the long-wave sensitivity of cones and the maximal optical density of the cornea at the same wavelengths. Comparison of the literature data on the spectral properties of photoreceptors and peculiarities of the cornea organization with the daily, seasonal, and other behavioral activities of greenlings allowed us to confirm the earlier proposal of an important light-protective role of the changeable cornea in greenlings.