Morphological and biochemical characterization of the cream markings in the integument of the female isopod, Armadillidium vulgare.

Cream markings aligned along the dorsal region of the female isopod, A. vulgare, were investigated with light and a fluorescence microscope and an electron microscope. Biochemical studies were also carried out. The cream markings were observed in the dorsal integument as a group of cream-colored chromatophores that emit a yellow fluorescence. These chromatophores, which are distinguishable from ommochrome chromatophores, contained numerous granules in the cytoplasm, and these granules (0.6-3.0 micron in length by 0.4-1.5 microns in width) were electron-lucent and spheroidal in shape with a concentric arrangement of membranes. Based on various biochemical analyses, the principal component of the yellow pigment isolated from the cream markings was identified as sepiapterin. These facts revealed that the cream markings are the chromatophores that contain pteridine granules. The males have no cream markings like those of the females, since the cream-colored chromatophores are externally hidden by the ommochrome chromatophore layer. The content of sepiapterin in the males was about two times greater than that in the females. This quantitative difference in sepiapterin content between males and females suggests that the pteridine formation in this pigment cell may be regulated by hormones associated with sex determination.