Live copepods (Tigriopus californicus) under diffuse, coaxial illumination (video) from Controlled iris radiance in a diurnal fish looking at prey

The recording demonstrates the reflectiveness of copepod ocelli. As can be seen, the reflected beam is not consistently sent back to the source, but sometimes also in other directions. Although this is not true retroreflection, the directionality and intensity of the reflection confirms a form of specular reflection, as expected for the guanine crystals that cover the inside of T. californicus cup-like ocelli [1] (see also ESM S1) (video by N.K.M.).1. Martin, G. G., Speekmann, C., Beidler, S. 2000 Photobehavior of the harpacticoid copepod Tigriopus californicus and the fine structure of its nauplius eye. Invertebr Biol. 119, 110-124. (10.1111/j.1744-7410.2000.tb00179.x)