Light-regulated body ion balance in marine slug Elysia viridis (Montagu)

Abstract

THE small, leaf-shaped marine slug Elysia viridis (Ophisto-branchia, Sacoglossa) owes its green colour to borrowed pigments. Unusual, although not unique in the animal kingdom, it is part of a ‘chloroplast symbiosis’ and is photosynthetically active. The chloroplasts, which are found in the cells of the highly branched digestive channel (hepatic diverticula), have been identified as originating from the siphonous green alga Codium fragile, on which Elysia feeds¹. Removed from its food source but kept in the light, Elysia can live for months by means of photosynthesis. In the dark, however, even when offered food, it soon dies². As part of the relationship the animal cells affect the morphological integrity and function of the symbiotic chloroplasts, and I report here that the cells themselves are influenced by the presense of the chloroplasts. The ion balance of Elysia is regulated by light through the mediation of the chloroplasts.