RHYTHMICITY OF CHROMOPHORE TURNOVER OF VISUAL PIGMENT IN THE ANTARCTIC AMPHIPOD ORCHOMENE-PLEBS (CRUSTACEA, AMPHIPODA)

1. Relative retinal amounts in the compound eye of the Antarctic amphi pod Orchomene plebs were assessed during conditions of continuous summ er daylight every 3 h over a period of 48 h. The habitat of the experi mental animal is the bottom of the Ross Sea (78-degrees-S; 166-degrees -E) down to depths of at least 400 m; water temperature is a constant - 1.8-degrees-C. A periodicity of 12 h was detected with relative amou nts of 11-cis retinal exhibiting peaks at midday and at midnight and t roughs at 7.00 h and 19.00 h. 2. The result that 90% of retinoid were insoluble in n-hexane suggests that at least 90% of the measured retin oid were attached to membrane-bound proteins such as opsin. 3. Selecti ve light adaptation showed that the visual pigments were thermostable and photoregenerable. The main absorbance peak of rhodopsin, compared with metarhodopsin, seems to be in the longer wavelengths.