ULTRASTRUCTURE OF THE PIGMENTARY SYSTEM AND CHROMATOPHOROTROPIC ACTIVITY IN LAND ISOPODS

¹ Departamento de Fisiologia, Instituto de Biociêncais e Instituto de Biologia Marinha, Universidade de Säo Paulo, P.O. Box 11176, Säo Paulo, Brazil

1. The question of the absence of physiological color change in terrestrial isopods was investigated with three species of land isopods (Armadillidium vulgare, Porcellio laevis and Pardioniscus argentinus) and a marine species (Ligia exotica) as reference.

2. The young and adults of the terrestrial isopods do not change color when exposed to dark or light conditions, nor to white or black backgrounds.

3. Light microscopy showed that the pigmentary System of the terrestrial isopods is an apparently syncytial net work containing a dark brown pigment.

4. Electron microscopy revealed that the pigmentary network is only apparently syncytial; its elements are merely contiguous. As compared to chromatophores of Ligia, the elements of the network of land isopods are much poorer in smooth endoplasmic reticulum and have no microtubules.

5. Homogenates of sinus gland and of nerve cord from land isopods induced pigment dispersion in melanophores from Ligia exotica; the effect was proportional to concentration of homogenate. Such extracts had no effect on melanophores of darkened animals.

6. The results obtained with the terrestrial species indicate that these isopods can produce chromatophorotropic-active substances (pigment-dispersing principles) despite their lack of physiological color change.

7. The lack of physiological color change is associated with the disappearance or absence of microtubules and reduction of endoplasmic reticulum, although there is no substantial evidence that these organelles play a role in pigment migration.