DIRECT DEVELOPMENT AND SYMBIOTIC CHLOROPLASTS IN ELYSIA TIMIDA (MOLLUSCA: OPISTHO BRANCHI A)

ABSTRACT

Elysia timida represents in its development an evolutionarily advanced type, as compared to other described Elysia. Egg number per egg mass is lowest, veliger stage and metamorphosis are completed inside the egg capsule, and a bilateral benthic juvenile hatches after 16–21 days. Mature E. timida contain symbiotic chloroplasts, which persist for two months and are then slowly bleached. Eggs and juveniles are aposymbiotic. Survival time of mature Elysia and juveniles in our cultures was four months and four weeks, respectively. Attempts to induce feeding on various algae, in juveniles or mature Elysia, were unsuccessful. Algal source of the symbiotic chloroplasts in E. timida and the mode of their acquisition remain unknown.