Morphology, molecular phylogeny and photosynthetic activity of the sacoglossan mollusc, Elysia nigrocapitata, from Korea

The morphology, external coloration as well as the life span of a kleptoplastic mollusc, Elysia nigrocapitata, was affected by its algal diet. Among algal diets, Chaetomorpha moniligera was the best for growth but not for animal longevity. TEM studies showed several distinctive layers composed of different cell types in sectioned parapodia. The chloroplast-containing digestive cells were located beneath the layer of vacuolated cells. The digestive cells contained 10–15 chloroplasts, in varying states of intactness, and several nuclei. Chloroplasts were not enclosed by any membranous structure in the host cytosol. Chlorophyll a fluorometry showed that the photosynthetic activity of kleptoplasts in E. nigrocapitata could be maintained for a long time only when animals were kept in the dark. The photosynthetic activity of kleptoplasts lasted 3–4 days when the animals were exposed to continuous illumination of 200 μmol photons m^?2 s^?1. These results suggested that the contribution of kleptoplasts to the survival of the animals might be minimal if the chloroplasts are not sequestered continuously. Cox I, 16S rDNA, and 28S rDNA sequence data have been obtained in order to phylogenetically place the new species of Elysia found in Korea.