| Summary: | The structure of the photoreceptors of three different Antarctic crustaceans was investigated by light and electron microscopy. Special attention was paid to light and temperature induced changes of the normal, i.e. dark-adapted eye. The apposition eye of Orchomene plebs shows structural modifications which are interpreted as adaptations to maximise photon capture in an environment of low ambient light intensities. Dark-light adaptational changes affect the position of the screening pigment granules, the volume of the random and the composition and density of the organelles in both retinula and interstitial cells. Exposure to a temperature of +10°c for seven hours affects the structural integrity of the rhabdoms and mimicks light-adaptation in animals that are kept in the dark. Rhabdoms regenerate as long as the animals are returned to water of 0°C. The ommatidia of the dorsal eye of Glyptonotus antarcticus possess very large diameters and are of the apposition type. Dark-light adaptational changes, which are confined to the dark eye if one eye is painted black and the other is left untouched, involve radial migration of screening pigment granules in the retinula cells surrounding the rhabdom. An elevation of the temperature also affects the position of the screening pigments, but the rhabdom ultrastructure is far less affected than that of Orchomene plebs. The compound eyes of the Ross Ice Shelf amphipod Orchomene grandis show the highest degree of structural adaptation to a dimly-lit environment. Following exposure to sunlight or darkness for one week at a temperature of approximately +1°C. the extraordinarily massive rhabdoms exhibit almost total disintegration. The density of screening pigment granules is so low that migrations upon dark-light adaptation are insignificant. The eye of Orchornene grandis shows the smallest capacity of all three species studied to adapt to different ambient light levels.
|
|---|