CHLOROPLAST SYMBIOSIS IN A NON-ELYSIID MOLLUSC, COSTASIELLA LILIANAE MARCUS (HERMAEIDAE: ASCOGLOSSA (=SACOGLOSSA): EFFECTS OF TEMPERATURE, LIGHT INTENSITY, AND STARVATION ON CARBON FIXATION RATE

¹ Department of Biological Sciences, Florida Institute of Technology, Melbourne, FL 32901

The hermaeid ascoglossan slug Costasiella lilianae possesses functional symbiotic chloroplasts derived from its algal food, Avrainvillea nigricans. Symbiotic plastids continued to fix carbon after 65 days starvation, though efficiency of fixation declined about 87%. Chlorophyll level did not decline during this period.

Degeneration of symbiotic plastids involved swelling and delamination of thylakoids, increase in electron density of plastids, and decrease in pyrenoid electron density. Plastids within single cells degenerate at about the same time, suggesting that individual cells phagocytize the entire complement of plastids during a brief period.

Temperature strongly influenced carbon fixation, both in rate of net fixation and in production of alcohol-insoluble photosynthates. The optimum temperature for fixation was 25°C. Photosynthetic rate exhibited saturation at about 500 µ\g=elunate\ (microeinsteins). m^-2 · s^-1 and substantial fixation occurred at intensities as low as 25 µ\g=elunate\ · m^-2 · s^-1. No inhibition occurred in full sunlight (1500 µ\g=elunate\ · m^-2 · s^-1).