Divisionistic generation of skin hue and the change of shade in the scalycheek damselfish, Pomacentrus lepidogenys

In addition to melanophores and xanthophores, there existed two types of iridophore in the dermis of the scalycheek damselfish, Pomacentrus lepidogenys. There are dendritic iridophores which reflect white light-rays by Tyndall scattering, and the round or somewhat ellipsoidal iridophores which reflect rays with a relatively narrow spectral peak from blue to green through the non-ideal thin-film interference. Most of the dendritic iridophores were covered with xanthophores and were situated over melanophores, thus constituting a kind of chromatophore unit which produces a yellow or yellowish-green color. The characteristic yellowish-green hue of the integument results from a compound effect of small contributions by more elementary colors. During color changes of the skin, the position of the spectral peak does not shift. Unlike the iridophores of the blue damselfish, both types of iridophore of the scalycheek damselfish were found to be inactive. It appears, therefore, that the aggregation and dispersion of pigment within the melanophores is the primary mechanism responsible for the changes in color of this species.