Cuticular microstructures and their relationship to structural color and transpiration in the terrestrial isopod Porcellionides pruinosus
The microstructure of the dorsal surface of the terrestrial isopod Porcellionides pruinosus was examined by scanning electron microscopy. Surface structures detected include sensory tricorns, spherical particles (balls) of various diameter, plates formed from the fusion of adjacent balls, and extremely small granules. A rod-shaped bacterium was also present on the surface of most individuals. The cuticular balls scatter and reflect incident light, producing a grayish white color or frosted appearance in most intermolt isopods. Prior to a molt, individuals are characteristically brown or unfrosted owing to the loss of the balls from the cuticle surface. New balls appear within a few hours following ecdysis and the isopod soon reacquires the frosted appearance. The balls are insoluble in lipid solvents and are also resistant to acetic acid and KOH. Higher water loss rates in unfrosted versus frosted individuals suggest that one function of the balls is to reduce cuticular transpiration in this species.