Average medial and lateral right eye parameters for two Phronima specimens based on measurements from micro-CT reconstructions.

Measurements are given as mean ± standard deviation. For each eye type, the average and standard deviation for facet diameter and rhabdom width were calculated from all ommatidia within the right eye of each specimen (N = 424 and 428 for the medial eyes and N = 261 and 265 for the lateral eyes), using these values, we then calculated the average between the two specimens (for both means and standard deviations). The average and standard deviation for focal length were calculated with a similar method but the measurements were taken from a subset of ommatidia within the right eye of each specimen (N = 50 for each eye type). Acceptance angles in degrees approximated using d/f using the average values of d and f (converted from radians; [36,37]). “No. ommatidia summated” represents the number of spatially summated neighbouring ommatidia.